The Descent of Man and Selection in Relation to Sex
by
Charles Darwin
Part 9 out of 17
whether in a state of nature or under confinement, are unanimously of
opinion that the males take delight in displaying their beauty. Audubon
frequently speaks of the male as endeavouring in various ways to charm the
female. Mr. Gould, after describing some peculiarities in a male humming-
bird, says he has no doubt that it has the power of displaying them to the
greatest advantage before the female. Dr. Jerdon (86. 'Birds of India,'
introduct., vol. i. p. xxiv.; on the peacock, vol. iii. p. 507. See
Gould's 'Introduction to Trochilidae,' 1861, pp. 15 and 111.) insists that
the beautiful plumage of the male serves "to fascinate and attract the
female." Mr. Bartlett, at the Zoological Gardens, expressed himself to me
in the strongest terms to the same effect.
[Fig. 50. Rupicola crocea, male (T.W. Wood).]
It must be a grand sight in the forests of India "to come suddenly on
twenty or thirty pea-fowl, the males displaying their gorgeous trains, and
strutting about in all the pomp of pride before the gratified females."
The wild turkey-cock erects his glittering plumage, expands his finely-
zoned tail and barred wing-feathers, and altogether, with his crimson and
blue wattles, makes a superb, though, to our eyes, grotesque appearance.
Similar facts have already been given with respect to grouse of various
kinds. Turning to another Order: The male Rupicola crocea (Fig. 50) is
one of the most beautiful birds in the world, being of a splendid orange,
with some of the feathers curiously truncated and plumose. The female is
brownish-green, shaded with red, and has a much smaller crest. Sir R.
Schomburgk has described their courtship; he found one of their meeting-
places where ten males and two females were present. The space was from
four to five feet in diameter, and appeared to have been cleared of every
blade of grass and smoothed as if by human hands. A male "was capering, to
the apparent delight of several others. Now spreading its wings, throwing
up its head, or opening its tail like a fan; now strutting about with a
hopping gait until tired, when it gabbled some kind of note, and was
relieved by another. Thus three of them successively took the field, and
then, with self-approbation, withdrew to rest." The Indians, in order to
obtain their skins, wait at one of the meeting-places till the birds are
eagerly engaged in dancing, and then are able to kill with their poisoned
arrows four or five males, one after the other. (87. 'Journal of R.
Geograph. Soc.' vol. x. 1840, p. 236.) With birds of paradise a dozen or
more full-plumaged males congregate in a tree to hold a dancing-party, as
it is called by the natives: and here they fly about, raise their wings,
elevate their exquisite plumes, and make them vibrate, and the whole tree
seems, as Mr. Wallace remarks, to be filled with waving plumes. When thus
engaged, they become so absorbed that a skilful archer may shoot nearly the
whole party. These birds, when kept in confinement in the Malay
Archipelago, are said to take much care in keeping their feathers clean;
often spreading them out, examining them, and removing every speck of dirt.
One observer, who kept several pairs alive, did not doubt that the display
of the male was intended to please the female. (88. 'Annals and Mag. of
Nat. Hist.' vol. xiii. 1854, p. 157; also Wallace, ibid. vol. xx. 1857, p.
412, and 'The Malay Archipelago,' vol. ii. 1869, p. 252. Also Dr. Bennett,
as quoted by Brehm, 'Thierleben,' B. iii. s. 326.)
[Fig. 51. Polyplectron chinquis, male (T.W. Wood).]
The Gold and Amherst pheasants during their courtship not only expand and
raise their splendid frills, but twist them, as I have myself seen,
obliquely towards the female on whichever side she may be standing,
obviously in order that a large surface may be displayed before her. (89.
Mr. T.W. Wood has given ('The Student,' April 1870, p. 115) a full account
of this manner of display, by the Gold pheasant and by the Japanese
pheasant, Ph. versicolor; and he calls it the lateral or one-sided
display.) They likewise turn their beautiful tails and tail-coverts a
little towards the same side. Mr. Bartlett has observed a male
Polyplectron (Fig. 51) in the act of courtship, and has shewn me a specimen
stuffed in the attitude then assumed. The tail and wing-feathers of this
bird are ornamented with beautiful ocelli, like those on the peacock's
train. Now when the peacock displays himself, he expands and erects his
tail transversely to his body, for he stands in front of the female, and
has to shew off, at the same time, his rich blue throat and breast. But
the breast of the Polyplectron is obscurely coloured, and the ocelli are
not confined to the tail-feathers. Consequently the Polyplectron does not
stand in front of the female; but he erects and expands his tail-feathers a
little obliquely, lowering the expanded wing on the same side, and raising
that on the opposite side. In this attitude the ocelli over the whole body
are exposed at the same time before the eyes of the admiring female in one
grand bespangled expanse. To whichever side she may turn, the expanded
wings and the obliquely-held tail are turned towards her. The male
Tragopan pheasant acts in nearly the same manner, for he raises the
feathers of the body, though not the wing itself, on the side which is
opposite to the female, and which would otherwise be concealed, so that
nearly all the beautifully spotted feathers are exhibited at the same time.
[Fig. 52. Side view of male Argus pheasant, whilst displaying before the
female. Observed and sketched from nature by T.W. Wood.]
The Argus pheasant affords a much more remarkable case. The immensely
developed secondary wing-feathers are confined to the male; and each is
ornamented with a row of from twenty to twenty-three ocelli, above an inch
in diameter. These feathers are also elegantly marked with oblique stripes
and rows of spots of a dark colour, like those on the skin of a tiger and
leopard combined. These beautiful ornaments are hidden until the male
shows himself off before the female. He then erects his tail, and expands
his wing-feathers into a great, almost upright, circular fan or shield,
which is carried in front of the body. The neck and head are held on one
side, so that they are concealed by the fan; but the bird in order to see
the female, before whom he is displaying himself, sometimes pushes his head
between two of the long wing-feathers (as Mr. Bartlett has seen), and then
presents a grotesque appearance. This must be a frequent habit with the
bird in a state of nature, for Mr. Bartlett and his son on examining some
perfect skins sent from the East, found a place between two of the feathers
which was much frayed, as if the head had here frequently been pushed
through. Mr. Wood thinks that the male can also peep at the female on one
side, beyond the margin of the fan.
The ocelli on the wing-feathers are wonderful objects; for they are so
shaded that, as the Duke of Argyll remarks (90. 'The Reign of Law,' 1867,
p. 203.), they stand out like balls lying loosely within sockets. When I
looked at the specimen in the British Museum, which is mounted with the
wings expanded and trailing downwards, I was however greatly disappointed,
for the ocelli appeared flat, or even concave. But Mr. Gould soon made the
case clear to me, for he held the feathers erect, in the position in which
they would naturally be displayed, and now, from the light shining on them
from above, each ocellus at once resembled the ornament called a ball and
socket. These feathers have been shown to several artists, and all have
expressed their admiration at the perfect shading. It may well be asked,
could such artistically shaded ornaments have been formed by means of
sexual selection? But it will be convenient to defer giving an answer to
this question until we treat in the next chapter of the principle of
gradation.
The foregoing remarks relate to the secondary wing-feathers, but the
primary wing-feathers, which in most gallinaceous birds are uniformly
coloured, are in the Argus pheasant equally wonderful. They are of a soft
brown tint with numerous dark spots, each of which consists of two or three
black dots with a surrounding dark zone. But the chief ornament is a space
parallel to the dark-blue shaft, which in outline forms a perfect second
feather lying within the true feather. This inner part is coloured of a
lighter chestnut, and is thickly dotted with minute white points. I have
shewn this feather to several persons, and many have admired it even more
than the ball and socket feathers, and have declared that it was more like
a work of art than of nature. Now these feathers are quite hidden on all
ordinary occasions, but are fully displayed, together with the long
secondary feathers, when they are all expanded together so as to form the
great fan or shield.
The case of the male Argus pheasant is eminently interesting, because it
affords good evidence that the most refined beauty may serve as a sexual
charm, and for no other purpose. We must conclude that this is the case,
as the secondary and primary wing-feathers are not at all displayed, and
the ball and socket ornaments are not exhibited in full perfection until
the male assumes the attitude of courtship. The Argus pheasant does not
possess brilliant colours, so that his success in love appears to depend on
the great size of his plumes, and on the elaboration of the most elegant
patterns. Many will declare that it is utterly incredible that a female
bird should be able to appreciate fine shading and exquisite patterns. It
is undoubtedly a marvellous fact that she should possess this almost human
degree of taste. He who thinks that he can safely gauge the discrimination
and taste of the lower animals may deny that the female Argus pheasant can
appreciate such refined beauty; but he will then be compelled to admit that
the extraordinary attitudes assumed by the male during the act of
courtship, by which the wonderful beauty of his plumage is fully displayed,
are purposeless; and this is a conclusion which I for one will never admit.
Although so many pheasants and allied gallinaceous birds carefully display
their plumage before the females, it is remarkable, as Mr. Bartlett informs
me, that this is not the case with the dull-coloured Eared and Cheer
pheasants (Crossoptilon auritum and Phasianus wallichii); so that these
birds seem conscious that they have little beauty to display. Mr. Bartlett
has never seen the males of either of these species fighting together,
though he has not had such good opportunities for observing the Cheer as
the Eared pheasant. Mr. Jenner Weir, also, finds that all male birds with
rich or strongly-characterised plumage are more quarrelsome than the dull-
coloured species belonging to the same groups. The goldfinch, for
instance, is far more pugnacious than the linnet, and the blackbird than
the thrush. Those birds which undergo a seasonal change of plumage
likewise become much more pugnacious at the period when they are most gaily
ornamented. No doubt the males of some obscurely-coloured birds fight
desperately together, but it appears that when sexual selection has been
highly influential, and has given bright colours to the males of any
species, it has also very often given a strong tendency to pugnacity. We
shall meet with nearly analogous cases when we treat of mammals. On the
other hand, with birds the power of song and brilliant colours have rarely
been both acquired by the males of the same species; but in this case the
advantage gained would have been the same, namely success in charming the
female. Nevertheless it must be owned that the males of several
brilliantly coloured birds have had their feathers specially modified for
the sake of producing instrumental music, though the beauty of this cannot
be compared, at least according to our taste, with that of the vocal music
of many songsters.
We will now turn to male birds which are not ornamented in any high degree,
but which nevertheless display during their courtship whatever attractions
they may possess. These cases are in some respects more curious than the
foregoing, and have been but little noticed. I owe the following facts to
Mr. Weir, who has long kept confined birds of many kinds, including all the
British Fringillidae and Emberizidae. The facts have been selected from a
large body of valuable notes kindly sent me by him. The bullfinch makes
his advances in front of the female, and then puffs out his breast, so that
many more of the crimson feathers are seen at once than otherwise would be
the case. At the same time he twists and bows his black tail from side to
side in a ludicrous manner. The male chaffinch also stands in front of the
female, thus shewing his red breast and "blue bell," as the fanciers call
his head; the wings at the same time being slightly expanded, with the pure
white bands on the shoulders thus rendered conspicuous. The common linnet
distends his rosy breast, slightly expands his brown wings and tail, so as
to make the best of them by exhibiting their white edgings. We must,
however, be cautious in concluding that the wings are spread out solely for
display, as some birds do so whose wings are not beautiful. This is the
case with the domestic cock, but it is always the wing on the side opposite
to the female which is expanded, and at the same time scraped on the
ground. The male goldfinch behaves differently from all other finches:
his wings are beautiful, the shoulders being black, with the dark-tipped
wing-feathers spotted with white and edged with golden yellow. When he
courts the female, he sways his body from side to side, and quickly turns
his slightly expanded wings first to one side, then to the other, with a
golden flashing effect. Mr. Weir informs me that no other British finch
turns thus from side to side during his courtship, not even the closely-
allied male siskin, for he would not thus add to his beauty.
Most of the British Buntings are plain coloured birds; but in the spring
the feathers on the head of the male reed-bunting (Emberiza schoeniculus)
acquire a fine black colour by the abrasion of the dusky tips; and these
are erected during the act of courtship. Mr. Weir has kept two species of
Amadina from Australia: the A. castanotis is a very small and chastely
coloured finch, with a dark tail, white rump, and jet-black upper tail-
coverts, each of the latter being marked with three large conspicuous oval
spots of white. (91. For the description of these birds, see Gould's
'Handbook to the Birds of Australia,' vol. i. 1865, p. 417.) This species,
when courting the female, slightly spreads out and vibrates these parti-
coloured tail-coverts in a very peculiar manner. The male Amadina Lathami
behaves very differently, exhibiting before the female his brilliantly
spotted breast, scarlet rump, and scarlet upper tail-coverts. I may here
add from Dr. Jerdon that the Indian bulbul (Pycnonotus hoemorrhous) has its
under tail-coverts of a crimson colour, and these, it might be thought,
could never be well exhibited; but the bird "when excited often spreads
them out laterally, so that they can be seen even from above." (92.
'Birds of India,' vol. ii. p. 96.) The crimson under tail-coverts of some
other birds, as with one of the woodpeckers, Picus major, can be seen
without any such display. The common pigeon has iridescent feathers on the
breast, and every one must have seen how the male inflates his breast
whilst courting the female, thus shewing them off to the best advantage.
One of the beautiful bronze-winged pigeons of Australia (Ocyphaps lophotes)
behaves, as described to me by Mr. Weir, very differently: the male,
whilst standing before the female, lowers his head almost to the ground,
spreads out and raises his tail, and half expands his wings. He then
alternately and slowly raises and depresses his body, so that the
iridescent metallic feathers are all seen at once, and glitter in the sun.
Sufficient facts have now been given to shew with what care male birds
display their various charms, and this they do with the utmost skill.
Whilst preening their feathers, they have frequent opportunities for
admiring themselves, and of studying how best to exhibit their beauty. But
as all the males of the same species display themselves in exactly the same
manner, it appears that actions, at first perhaps intentional, have become
instinctive. If so, we ought not to accuse birds of conscious vanity; yet
when we see a peacock strutting about, with expanded and quivering tail-
feathers, he seems the very emblem of pride and vanity.
The various ornaments possessed by the males are certainly of the highest
importance to them, for in some cases they have been acquired at the
expense of greatly impeded powers of flight or of running. The African
night-jar (Cosmetornis), which during the pairing-season has one of its
primary wing-feathers developed into a streamer of very great length, is
thereby much retarded in its flight, although at other times remarkable for
its swiftness. The "unwieldy size" of the secondary wing-feathers of the
male Argus pheasant is said "almost entirely to deprive the bird of
flight." The fine plumes of male birds of paradise trouble them during a
high wind. The extremely long tail-feathers of the male widow-birds
(Vidua) of Southern Africa render "their flight heavy;" but as soon as
these are cast off they fly as well as the females. As birds always breed
when food is abundant, the males probably do not suffer much inconvenience
in searching for food from their impeded powers of movement; but there can
hardly be a doubt that they must be much more liable to be struck down by
birds of prey. Nor can we doubt that the long train of the peacock and the
long tail and wing-feathers of the Argus pheasant must render them an
easier prey to any prowling tiger-cat than would otherwise be the case.
Even the bright colours of many male birds cannot fail to make them
conspicuous to their enemies of all kinds. Hence, as Mr. Gould has
remarked, it probably is that such birds are generally of a shy
disposition, as if conscious that their beauty was a source of danger, and
are much more difficult to discover or approach, than the sombre coloured
and comparatively tame females or than the young and as yet unadorned
males. (93. On the Cosmetornis, see Livingstone's 'Expedition to the
Zambesi,' 1865, p. 66. On the Argus pheasant, Jardine's 'Nat. Hist. Lib.:
Birds,' vol. xiv. p. 167. On Birds of Paradise, Lesson, quoted by Brehm,
'Thierleben,' B. iii. s. 325. On the widow-bird, Barrow's 'Travels in
Africa,' vol. i. p. 243, and 'Ibis,' vol. iii. 1861 p. 133. Mr. Gould, on
the shyness of male birds, 'Handbook to Birds of Australia,' vol. i. 1865,
pp. 210, 457.)
It is a more curious fact that the males of some birds which are provided
with special weapons for battle, and which in a state of nature are so
pugnacious that they often kill each other, suffer from possessing certain
ornaments. Cock-fighters trim the hackles and cut off the combs and gills
of their cocks; and the birds are then said to be dubbed. An undubbed
bird, as Mr. Tegetmeier insists, "is at a fearful disadvantage; the comb
and gills offer an easy hold to his adversary's beak, and as a cock always
strikes where he holds, when once he has seized his foe, he has him
entirely in his power. Even supposing that the bird is not killed, the
loss of blood suffered by an undubbed cock is much greater than that
sustained by one that has been trimmed." (94. Tegetmeier, 'The Poultry
Book,' 1866, p. 139.) Young turkey-cocks in fighting always seize hold of
each other's wattles; and I presume that the old birds fight in the same
manner. It may perhaps be objected that the comb and wattles are not
ornamental, and cannot be of service to the birds in this way; but even to
our eyes, the beauty of the glossy black Spanish cock is much enhanced by
his white face and crimson comb; and no one who has ever seen the splendid
blue wattles of the male Tragopan pheasant distended in courtship can for a
moment doubt that beauty is the object gained. From the foregoing facts we
clearly see that the plumes and other ornaments of the males must be of the
highest importance to them; and we further see that beauty is even
sometimes more important than success in battle.
CHAPTER XIV.
BIRDS--continued.
Choice exerted by the female--Length of courtship--Unpaired birds--Mental
qualities and taste for the beautiful--Preference or antipathy shewn by the
female for particular males--Variability of birds--Variations sometimes
abrupt--Laws of variation--Formation of ocelli--Gradations of character--
Case of Peacock, Argus pheasant, and Urosticte.
When the sexes differ in beauty or in the power of singing, or in producing
what I have called instrumental music, it is almost invariably the male who
surpasses the female. These qualities, as we have just seen, are evidently
of high importance to the male. When they are gained for only a part of
the year it is always before the breeding-season. It is the male alone who
elaborately displays his varied attractions, and often performs strange
antics on the ground or in the air, in the presence of the female. Each
male drives away, or if he can, kills his rivals. Hence we may conclude
that it is the object of the male to induce the female to pair with him,
and for this purpose he tries to excite or charm her in various ways; and
this is the opinion of all those who have carefully studied the habits of
living birds. But there remains a question which has an all important
bearing on sexual selection, namely, does every male of the same species
excite and attract the female equally? Or does she exert a choice, and
prefer certain males? This latter question can be answered in the
affirmative by much direct and indirect evidence. It is far more difficult
to decide what qualities determine the choice of the females; but here
again we have some direct and indirect evidence that it is to a large
extent the external attractions of the male; though no doubt his vigour,
courage, and other mental qualities come into play. We will begin with the
indirect evidence.
LENGTH OF COURTSHIP.
The lengthened period during which both sexes of certain birds meet day
after day at an appointed place probably depends partly on the courtship
being a prolonged affair, and partly on reiteration in the act of pairing.
Thus in Germany and Scandinavia the balzen or leks of the black-cocks last
from the middle of March, all through April into May. As many as forty or
fifty, or even more birds congregate at the leks; and the same place is
often frequented during successive years. The lek of the capercailzie
lasts from the end of March to the middle or even end of May. In North
America "the partridge dances" of the Tetrao phasianellus "last for a month
or more." Other kinds of grouse, both in North America and Eastern Siberia
(1. Nordman describes ('Bull. Soc. Imp. des Nat. Moscou,' 1861, tom.
xxxiv. p. 264) the balzen of Tetrao urogalloides in Amur Land. He
estimated the number of birds assembled at above a hundred, not counting
the females, which lie hid in the surrounding bushes. The noises uttered
differ from those of T. urogallus.), follow nearly the same habits. The
fowlers discover the hillocks where the ruffs congregate by the grass being
trampled bare, and this shews that the same spot is long frequented. The
Indians of Guiana are well acquainted with the cleared arenas, where they
expect to find the beautiful cocks of the Rock; and the natives of New
Guinea know the trees where from ten to twenty male birds of paradise in
full plumage congregate. In this latter case it is not expressly stated
that the females meet on the same trees, but the hunters, if not specially
asked, would probably not mention their presence, as their skins are
valueless. Small parties of an African weaver (Ploceus) congregate, during
the breeding-season, and perform for hours their graceful evolutions.
Large numbers of the Solitary snipe (Scolopax major) assemble during dusk
in a morass; and the same place is frequented for the same purpose during
successive years; here they may be seen running about "like so many large
rats," puffing out their feathers, flapping their wings, and uttering the
strangest cries. (2. With respect to the assemblages of the above named
grouse, see Brehm, 'Thierleben,' B. iv. s. 350; also L. Lloyd, 'Game Birds
of Sweden,' 1867, pp. 19, 78. Richardson, 'Fauna Bor. Americana: Birds,'
p. 362. References in regard to the assemblages of other birds have
already been given. On Paradisea, see Wallace, in 'Annals and Mag. of Nat.
Hist.' vol. xx. 1857, p. 412. On the snipe, Lloyd, ibid. p. 221.)
Some of the above birds,--the black-cock, capercailzie, pheasant-grouse,
ruff, solitary snipe, and perhaps others,--are, as is believed,
polygamists. With such birds it might have been thought that the stronger
males would simply have driven away the weaker, and then at once have taken
possession of as many females as possible; but if it be indispensable for
the male to excite or please the female, we can understand the length of
the courtship and the congregation of so many individuals of both sexes at
the same spot. Certain strictly monogamous species likewise hold nuptial
assemblages; this seems to be the case in Scandinavia with one of the
ptarmigans, and their leks last from the middle of March to the middle of
May. In Australia the lyre-bird (Menura superba) forms "small round
hillocks," and the M. Alberti scratches for itself shallow holes, or, as
they are called by the natives, "corroborying places," where it is believed
both sexes assemble. The meetings of the M. superba are sometimes very
large; and an account has lately been published (3. Quoted by Mr. T.W.
Wood, in the 'Student,' April 1870, p. 125.) by a traveller, who heard in a
valley beneath him, thickly covered with scrub, "a din which completely
astonished" him; on crawling onwards he beheld, to his amazement, about one
hundred and fifty of the magnificent lyre-cocks, "ranged in order of
battle, and fighting with indescribable fury." The bowers of the Bower-
birds are the resort of both sexes during the breeding-season; and "here
the males meet and contend with each other for the favours of the female,
and here the latter assemble and coquet with the males." With two of the
genera, the same bower is resorted to during many years. (4. Gould,
'Handbook to the Birds of Australia,' vol. i. pp. 300, 308, 448, 451. On
the ptarmigan, above alluded to, see Lloyd, ibid. p. 129.)
The common magpie (Corvus pica, Linn.), as I have been informed by the Rev.
W. Darwin Fox, used to assemble from all parts of Delamere Forest, in order
to celebrate the "great magpie marriage." Some years ago these birds
abounded in extraordinary numbers, so that a gamekeeper killed in one
morning nineteen males, and another killed by a single shot seven birds at
roost together. They then had the habit of assembling very early in the
spring at particular spots, where they could be seen in flocks, chattering,
sometimes fighting, bustling and flying about the trees. The whole affair
was evidently considered by the birds as one of the highest importance.
Shortly after the meeting they all separated, and were then observed by Mr.
Fox and others to be paired for the season. In any district in which a
species does not exist in large numbers, great assemblages cannot, of
course, be held, and the same species may have different habits in
different countries. For instance, I have heard of only one instance, from
Mr. Wedderburn, of a regular assemblage of black game in Scotland, yet
these assemblages are so well known in Germany and Scandinavia that they
have received special names.
UNPAIRED BIRDS.
From the facts now given, we may conclude that the courtship of birds
belonging to widely different groups, is often a prolonged, delicate, and
troublesome affair. There is even reason to suspect, improbable as this
will at first appear, that some males and females of the same species,
inhabiting the same district, do not always please each other, and
consequently do not pair. Many accounts have been published of either the
male or female of a pair having been shot, and quickly replaced by another.
This has been observed more frequently with the magpie than with any other
bird, owing perhaps to its conspicuous appearance and nest. The
illustrious Jenner states that in Wiltshire one of a pair was daily shot no
less than seven times successively, "but all to no purpose, for the
remaining magpie soon found another mate"; and the last pair reared their
young. A new partner is generally found on the succeeding day; but Mr.
Thompson gives the case of one being replaced on the evening of the same
day. Even after the eggs are hatched, if one of the old birds is destroyed
a mate will often be found; this occurred after an interval of two days, in
a case recently observed by one of Sir J. Lubbock's keepers. (5. On
magpies, Jenner, in 'Philosophical Transactions,' 1824, p. 21.
Macgillivray, 'Hist. British Birds,' vol. i. p. 570. Thompson, in 'Annals
and Magazine of Natural History,' vol. viii. 1842, p. 494.) The first and
most obvious conjecture is that male magpies must be much more numerous
than females; and that in the above cases, as well as in many others which
could be given, the males alone had been killed. This apparently holds
good in some instances, for the gamekeepers in Delamere Forest assured Mr.
Fox that the magpies and carrion-crows which they formerly killed in
succession in large numbers near their nests, were all males; and they
accounted for this fact by the males being easily killed whilst bringing
food to the sitting females. Macgillivray, however, gives, on the
authority of an excellent observer, an instance of three magpies
successively killed on the same nest, which were all females; and another
case of six magpies successively killed whilst sitting on the same eggs,
which renders it probable that most of them were females; though, as I hear
from Mr. Fox, the male will sit on the eggs when the female is killed.
Sir J. Lubbock's gamekeeper has repeatedly shot, but how often he could not
say, one of a pair of jays (Garrulus glandarius), and has never failed
shortly afterwards to find the survivor re-matched. Mr. Fox, Mr. F. Bond,
and others have shot one of a pair of carrion-crows (Corvus corone), but
the nest was soon again tenanted by a pair. These birds are rather common;
but the peregrine-falcon (Falco peregrinus) is rare, yet Mr. Thompson
states that in Ireland "if either an old male or female be killed in the
breeding-season (not an uncommon circumstance), another mate is found
within a very few days, so that the eyries, notwithstanding such
casualties, are sure to turn out their complement of young." Mr. Jenner
Weir has known the same thing with the peregrine-falcons at Beachy Head.
The same observer informs me that three kestrels (Falco tinnunculus), all
males, were killed one after the other whilst attending the same nest; two
of these were in mature plumage, but the third was in the plumage of the
previous year. Even with the rare golden eagle (Aquila chrysaetos), Mr.
Birkbeck was assured by a trustworthy gamekeeper in Scotland, that if one
is killed, another is soon found. So with the white owl (Strix flammea),
"the survivor readily found a mate, and the mischief went on."
White of Selborne, who gives the case of the owl, adds that he knew a man,
who from believing that partridges when paired were disturbed by the males
fighting, used to shoot them; and though he had widowed the same female
several times, she always soon found a fresh partner. This same naturalist
ordered the sparrows, which deprived the house-martins of their nests, to
be shot; but the one which was left, "be it cock or hen, presently procured
a mate, and so for several times following." I could add analogous cases
relating to the chaffinch, nightingale, and redstart. With respect to the
latter bird (Phoenicura ruticilla), a writer expresses much surprise how
the sitting female could so soon have given effectual notice that she was a
widow, for the species was not common in the neighbourhood. Mr. Jenner
Weir has mentioned to me a nearly similar case; at Blackheath he never sees
or hears the note of the wild bullfinch, yet when one of his caged males
has died, a wild one in the course of a few days has generally come and
perched near the widowed female, whose call-note is not loud. I will give
only one other fact, on the authority of this same observer; one of a pair
of starlings (Sturnus vulgaris) was shot in the morning; by noon a new mate
was found; this was again shot, but before night the pair was complete; so
that the disconsolate widow or widower was thrice consoled during the same
day. Mr. Engleheart also informs me that he used during several years to
shoot one of a pair of starlings which built in a hole in a house at
Blackheath; but the loss was always immediately repaired. During one
season he kept an account, and found that he had shot thirty-five birds
from the same nest; these consisted of both males and females, but in what
proportion he could not say: nevertheless, after all this destruction, a
brood was reared. (6. On the peregrine falcon, see Thompson, 'Nat. Hist.
of Ireland: Birds,' vol. i. 1849, p. 39. On owls, sparrows, and
partridges, see White, 'Nat. Hist. of Selborne,' edit. of 1825, vol. i. p.
139. On the Phoenicura, see Loudon's 'Mag. of Nat. Hist.' vol. vii. 1834,
p. 245. Brehm ('Thierleben,' B. iv. s. 991) also alludes to cases of birds
thrice mated during the same day.)
These facts well deserve attention. How is it that there are birds enough
ready to replace immediately a lost mate of either sex? Magpies, jays,
carrion-crows, partridges, and some other birds, are always seen during the
spring in pairs, and never by themselves; and these offer at first sight
the most perplexing cases. But birds of the same sex, although of course
not truly paired, sometimes live in pairs or in small parties, as is known
to be the case with pigeons and partridges. Birds also sometimes live in
triplets, as has been observed with starlings, carrion-crows, parrots, and
partridges. With partridges two females have been known to live with one
male, and two males with one female. In all such cases it is probable that
the union would be easily broken; and one of the three would readily pair
with a widow or widower. The males of certain birds may occasionally be
heard pouring forth their love-song long after the proper time, shewing
that they have either lost or never gained a mate. Death from accident or
disease of one of a pair would leave the other free and single; and there
is reason to believe that female birds during the breeding-season are
especially liable to premature death. Again, birds which have had their
nests destroyed, or barren pairs, or retarded individuals, would easily be
induced to desert their mates, and would probably be glad to take what
share they could of the pleasures and duties of rearing offspring although
not their own. (7. See White ('Nat. Hist. of Selborne,' 1825, vol. i. p.
140) on the existence, early in the season, of small coveys of male
partridges, of which fact I have heard other instances. See Jenner, on the
retarded state of the generative organs in certain birds, in 'Phil.
Transact.' 1824. In regard to birds living in triplets, I owe to Mr.
Jenner Weir the cases of the starlings and parrots, and to Mr. Fox, of
partridges; on carrion-crows, see the 'Field,' 1868, p. 415. On various
male birds singing after the proper period, see Rev. L. Jenyns,
'Observations in Natural History,' 1846, p. 87.) Such contingencies as
these probably explain most of the foregoing cases. (8. The following
case has been given ('The Times,' Aug. 6, 1868) by the Rev. F.O. Morris, on
the authority of the Hon. and Rev. O.W. Forester. "The gamekeeper here
found a hawk's nest this year, with five young ones on it. He took four
and killed them, but left one with its wings clipped as a decoy to destroy
the old ones by. They were both shot next day, in the act of feeding the
young one, and the keeper thought it was done with. The next day he came
again and found two other charitable hawks, who had come with an adopted
feeling to succour the orphan. These two he killed, and then left the
nest. On returning afterwards he found two more charitable individuals on
the same errand of mercy. One of these he killed; the other he also shot,
but could not find. No more came on the like fruitless errand.")
Nevertheless, it is a strange fact that within the same district, during
the height of the breeding-season, there should be so many males and
females always ready to repair the loss of a mated bird. Why do not such
spare birds immediately pair together? Have we not some reason to suspect,
and the suspicion has occurred to Mr. Jenner Weir, that as the courtship of
birds appears to be in many cases prolonged and tedious, so it occasionally
happens that certain males and females do not succeed, during the proper
season, in exciting each other's love, and consequently do not pair? This
suspicion will appear somewhat less improbable after we have seen what
strong antipathies and preferences female birds occasionally evince towards
particular males.
MENTAL QUALITIES OF BIRDS, AND THEIR TASTE FOR THE BEAUTIFUL.
Before we further discuss the question whether the females select the more
attractive males or accept the first whom they may encounter, it will be
advisable briefly to consider the mental powers of birds. Their reason is
generally, and perhaps justly, ranked as low; yet some facts could be given
leading to an opposite conclusion. (9. I am indebted to Prof. Newton for
the following passage from Mr. Adam's 'Travels of a Naturalist,' 1870, p.
278. Speaking of Japanese nut-hatches in confinement, he says: "Instead
of the more yielding fruit of the yew, which is the usual food of the nut-
hatch of Japan, at one time I substituted hard hazel-nuts. As the bird was
unable to crack them, he placed them one by one in his water-glass,
evidently with the notion that they would in time become softer--an
interesting proof of intelligence on the part of these birds.") Low powers
of reasoning, however, are compatible, as we see with mankind, with strong
affections, acute perception, and a taste for the beautiful; and it is with
these latter qualities that we are here concerned. It has often been said
that parrots become so deeply attached to each other that when one dies the
other pines for a long time; but Mr. Jenner Weir thinks that with most
birds the strength of their affection has been much exaggerated.
Nevertheless when one of a pair in a state of nature has been shot, the
survivor has been heard for days afterwards uttering a plaintive call; and
Mr. St. John gives various facts proving the attachment of mated birds.
(10. 'A Tour in Sutherlandshire,' vol. i. 1849, p. 185. Dr. Buller says
('Birds of New Zealand,' 1872, p. 56) that a male King Lory was killed; and
the female "fretted and moped, refused her food, and died of a broken
heart.") Mr. Bennett relates (11. 'Wanderings in New South Wales,' vol.
ii. 1834, p. 62.) that in China after a drake of the beautiful mandarin
Teal had been stolen, the duck remained disconsolate, though sedulously
courted by another mandarin drake, who displayed before her all his charms.
After an interval of three weeks the stolen drake was recovered, and
instantly the pair recognised each other with extreme joy. On the other
hand, starlings, as we have seen, may be consoled thrice in the same day
for the loss of their mates. Pigeons have such excellent local memories,
that they have been known to return to their former homes after an interval
of nine months, yet, as I hear from Mr. Harrison Weir, if a pair which
naturally would remain mated for life be separated for a few weeks during
the winter, and afterwards matched with other birds, the two when brought
together again, rarely, if ever, recognise each other.
Birds sometimes exhibit benevolent feelings; they will feed the deserted
young ones even of distinct species, but this perhaps ought to be
considered as a mistaken instinct. They will feed, as shewn in an earlier
part of this work, adult birds of their own species which have become
blind. Mr. Buxton gives a curious account of a parrot which took care of a
frost-bitten and crippled bird of a distinct species, cleansed her
feathers, and defended her from the attacks of the other parrots which
roamed freely about his garden. It is a still more curious fact that these
birds apparently evince some sympathy for the pleasures of their fellows.
When a pair of cockatoos made a nest in an acacia tree, "it was ridiculous
to see the extravagant interest taken in the matter by the others of the
same species." These parrots, also, evinced unbounded curiosity, and
clearly had "the idea of property and possession." (12. 'Acclimatization
of Parrots,' by C. Buxton, M.P., 'Annals and Mag. of Nat. Hist.' Nov. 1868,
p. 381.) They have good memories, for in the Zoological Gardens they have
plainly recognised their former masters after an interval of some months.
Birds possess acute powers of observation. Every mated bird, of course,
recognises its fellow. Audubon states that a certain number of mocking-
thrushes (Mimus polyglottus) remain all the year round in Louisiana, whilst
others migrate to the Eastern States; these latter, on their return, are
instantly recognised, and always attacked, by their southern brethren.
Birds under confinement distinguish different persons, as is proved by the
strong and permanent antipathy or affection which they shew, without any
apparent cause, towards certain individuals. I have heard of numerous
instances with jays, partridges, canaries, and especially bullfinches. Mr.
Hussey has described in how extraordinary a manner a tamed partridge
recognised everybody: and its likes and dislikes were very strong. This
bird seemed "fond of gay colours, and no new gown or cap could be put on
without catching his attention." (13. The 'Zoologist,' 1847-48, p. 1602.)
Mr. Hewitt has described the habits of some ducks (recently descended from
wild birds), which, at the approach of a strange dog or cat, would rush
headlong into the water, and exhaust themselves in their attempts to
escape; but they knew Mr. Hewitt's own dogs and cats so well that they
would lie down and bask in the sun close to them. They always moved away
from a strange man, and so they would from the lady who attended them if
she made any great change in her dress. Audubon relates that he reared and
tamed a wild turkey which always ran away from any strange dog; this bird
escaped into the woods, and some days afterwards Audubon saw, as he
thought, a wild turkey, and made his dog chase it; but, to his
astonishment, the bird did not run away, and the dog, when he came up, did
not attack the bird, for they mutually recognised each other as old
friends. (14. Hewitt on wild ducks, 'Journal of Horticulture,' Jan. 13,
1863, p. 39. Audubon on the wild turkey, 'Ornithological Biography,' vol.
i. p. 14. On the mocking-thrush, ibid. vol. i. p. 110.)
Mr. Jenner Weir is convinced that birds pay particular attention to the
colours of other birds, sometimes out of jealousy, and sometimes as a sign
of kinship. Thus he turned a reed-bunting (Emberiza schoeniculus), which
had acquired its black head-dress, into his aviary, and the new-comer was
not noticed by any bird, except by a bullfinch, which is likewise black-
headed. This bullfinch was a very quiet bird, and had never before
quarrelled with any of its comrades, including another reed-bunting, which
had not as yet become black-headed: but the reed-bunting with a black head
was so unmercifully treated that it had to be removed. Spiza cyanea,
during the breeding-season, is of a bright blue colour; and though
generally peaceable, it attacked S. ciris, which has only the head blue,
and completely scalped the unfortunate bird. Mr. Weir was also obliged to
turn out a robin, as it fiercely attacked all the birds in his aviary with
any red in their plumage, but no other kinds; it actually killed a red-
breasted crossbill, and nearly killed a goldfinch. On the other band, he
has observed that some birds, when first introduced, fly towards the
species which resemble them most in colour, and settle by their sides.
As male birds display their fine plumage and other ornaments with so much
care before the females, it is obviously probable that these appreciate the
beauty of their suitors. It is, however, difficult to obtain direct
evidence of their capacity to appreciate beauty. When birds gaze at
themselves in a looking-glass (of which many instances have been recorded)
we cannot feel sure that it is not from jealousy of a supposed rival,
though this is not the conclusion of some observers. In other cases it is
difficult to distinguish between mere curiosity and admiration. It is
perhaps the former feeling which, as stated by Lord Lilford (15. The
'Ibis,' vol. ii. 1860, p. 344.), attracts the ruff towards any bright
object, so that, in the Ionian Islands, "it will dart down to a bright-
coloured handkerchief, regardless of repeated shots." The common lark is
drawn down from the sky, and is caught in large numbers, by a small mirror
made to move and glitter in the sun. Is it admiration or curiosity which
leads the magpie, raven, and some other birds to steal and secrete bright
objects, such as silver articles or jewels?
Mr. Gould states that certain humming-birds decorate the outsides of their
nests "with the utmost taste; they instinctively fasten thereon beautiful
pieces of flat lichen, the larger pieces in the middle, and the smaller on
the part attached to the branch. Now and then a pretty feather is
intertwined or fastened to the outer sides, the stem being always so placed
that the feather stands out beyond the surface." The best evidence,
however, of a taste for the beautiful is afforded by the three genera of
Australian bower-birds already mentioned. Their bowers (Fig. 46), where
the sexes congregate and play strange antics, are variously constructed,
but what most concerns us is, that they are decorated by the several
species in a different manner. The Satin bower-bird collects gaily-
coloured articles, such as the blue tail-feathers of parrakeets, bleached
bones and shells, which it sticks between the twigs or arranges at the
entrance. Mr. Gould found in one bower a neatly-worked stone tomahawk and
a slip of blue cotton, evidently procured from a native encampment. These
objects are continually re-arranged, and carried about by the birds whilst
at play. The bower of the Spotted bower-bird "is beautifully lined with
tall grasses, so disposed that the heads nearly meet, and the decorations
are very profuse." Round stones are used to keep the grass-stems in their
proper places, and to make divergent paths leading to the bower. The
stones and shells are often brought from a great distance. The Regent
bird, as described by Mr. Ramsay, ornaments its short bower with bleached
land-shells belonging to five or six species, and with "berries of various
colours, blue, red, and black, which give it when fresh a very pretty
appearance. Besides these there were several newly-picked leaves and young
shoots of a pinkish colour, the whole showing a decided taste for the
beautiful." Well may Mr. Gould say that "these highly decorated halls of
assembly must be regarded as the most wonderful instances of bird-
architecture yet discovered;" and the taste, as we see, of the several
species certainly differs. (16. On the ornamented nests of humming-birds,
Gould, 'Introduction to the Trochilidae,' 1861, p. 19. On the bower-birds,
Gould, 'Handbook to the Birds of Australia,' 1865, vol. i. pp. 444-461.
Ramsay, in the 'Ibis,' 1867, p. 456.)
PREFERENCE FOR PARTICULAR MALES BY THE FEMALES.
Having made these preliminary remarks on the discrimination and taste of
birds, I will give all the facts known to me which bear on the preference
shewn by the female for particular males. It is certain that distinct
species of birds occasionally pair in a state of nature and produce
hybrids. Many instances could be given: thus Macgillivray relates how a
male blackbird and female thrush "fell in love with each other," and
produced offspring. (17. 'History of Brit. Birds,' vol. ii. p. 92.)
Several years ago eighteen cases had been recorded of the occurrence in
Great Britain of hybrids between the black grouse and pheasant (18.
'Zoologist,' 1853-1854, p. 3946.); but most of these cases may perhaps be
accounted for by solitary birds not finding one of their own species to
pair with. With other birds, as Mr. Jenner Weir has reason to believe,
hybrids are sometimes the result of the casual intercourse of birds
building in close proximity. But these remarks do not apply to the many
recorded instances of tamed or domestic birds, belonging to distinct
species, which have become absolutely fascinated with each other, although
living with their own species. Thus Waterton (19. Waterton, 'Essays on
Nat. Hist.' 2nd series, pp. 42 and 117. For the following statements see
on the wigeon, 'Loudon's Mag. of Nat. Hist.' vol. ix. p. 616; L. Lloyd,
'Scandinavian Adventures,' vol. i. 1854, p. 452. Dixon, 'Ornamental and
Domestic Poultry,' p. 137; Hewitt, in 'Journal of Horticulture,' Jan. 13,
1863, p. 40; Bechstein, 'Stubenvogel,' 1840, s. 230. Mr. J. Jenner Weir
has lately given me an analogous case with ducks of two species.) states
that out of a flock of twenty-three Canada geese, a female paired with a
solitary Bernicle gander, although so different in appearance and size; and
they produced hybrid offspring. A male wigeon (Mareca penelope), living
with females of the same species, has been known to pair with a pintail
duck, Querquedula acuta. Lloyd describes the remarkable attachment between
a shield-drake (Tadorna vulpanser) and a common duck. Many additional
instances could be given; and the Rev. E.S. Dixon remarks that "those who
have kept many different species of geese together well know what
unaccountable attachments they are frequently forming, and that they are
quite as likely to pair and rear young with individuals of a race (species)
apparently the most alien to themselves as with their own stock."
The Rev. W.D. Fox informs me that he possessed at the same time a pair of
Chinese geese (Anser cygnoides), and a common gander with three geese. The
two lots kept quite separate, until the Chinese gander seduced one of the
common geese to live with him. Moreover, of the young birds hatched from
the eggs of the common geese, only four were pure, the other eighteen
proving hybrids; so that the Chinese gander seems to have had prepotent
charms over the common gander. I will give only one other case; Mr. Hewitt
states that a wild duck, reared in captivity, "after breeding a couple of
seasons with her own mallard, at once shook him off on my placing a male
Pintail on the water. It was evidently a case of love at first sight, for
she swam about the new-comer caressingly, though he appeared evidently
alarmed and averse to her overtures of affection. From that hour she
forgot her old partner. Winter passed by, and the next spring the pintail
seemed to have become a convert to her blandishments, for they nested and
produced seven or eight young ones."
What the charm may have been in these several cases, beyond mere novelty,
we cannot even conjecture. Colour, however, sometimes comes into play; for
in order to raise hybrids from the siskin (Fringilla spinus) and the
canary, it is much the best plan, according to Bechstein, to place birds of
the same tint together. Mr. Jenner Weir turned a female canary into his
aviary, where there were male linnets, goldfinches, siskins, greenfinches,
chaffinches, and other birds, in order to see which she would choose; but
there never was any doubt, and the greenfinch carried the day. They paired
and produced hybrid offspring.
The fact of the female preferring to pair with one male rather than with
another of the same species is not so likely to excite attention, as when
this occurs, as we have just seen, between distinct species. The former
cases can best be observed with domesticated or confined birds; but these
are often pampered by high feeding, and sometimes have their instincts
vitiated to an extreme degree. Of this latter fact I could give sufficient
proofs with pigeons, and especially with fowls, but they cannot be here
related. Vitiated instincts may also account for some of the hybrid unions
above mentioned; but in many of these cases the birds were allowed to range
freely over large ponds, and there is no reason to suppose that they were
unnaturally stimulated by high feeding.
With respect to birds in a state of nature, the first and most obvious
supposition which will occur to every one is that the female at the proper
season accepts the first male whom she may encounter; but she has at least
the opportunity for exerting a choice, as she is almost invariably pursued
by many males. Audubon--and we must remember that he spent a long life in
prowling about the forests of the United States and observing the birds--
does not doubt that the female deliberately chooses her mate; thus,
speaking of a woodpecker, he says the hen is followed by half-a-dozen gay
suitors, who continue performing strange antics, "until a marked preference
is shewn for one." The female of the red-winged starling (Agelaeus
phoeniceus) is likewise pursued by several males, "until, becoming
fatigued, she alights, receives their addresses, and soon makes a choice."
He describes also how several male night-jars repeatedly plunge through the
air with astonishing rapidity, suddenly turning, and thus making a singular
noise; "but no sooner has the female made her choice than the other males
are driven away." With one of the vultures (Cathartes aura) of the United
States, parties of eight, ten, or more males and females assemble on fallen
logs, "exhibiting the strongest desire to please mutually," and after many
caresses, each male leads off his partner on the wing. Audubon likewise
carefully observed the wild flocks of Canada geese (Anser canadensis), and
gives a graphic description of their love-antics; he says that the birds
which had been previously mated "renewed their courtship as early as the
month of January, while the others would be contending or coquetting for
hours every day, until all seemed satisfied with the choice they had made,
after which, although they remained together, any person could easily
perceive that they were careful to keep in pairs. I have observed also
that the older the birds the shorter were the preliminaries of their
courtship. The bachelors and old maids whether in regret, or not caring to
be disturbed by the bustle, quietly moved aside and lay down at some
distance from the rest." (20. Audubon, 'Ornithological Biography,' vol.
i. pp. 191, 349; vol. ii. pp. 42, 275; vol. iii. p. 2.) Many similar
statements with respect to other birds could be cited from this same
observer.
Turning now to domesticated and confined birds, I will commence by giving
what little I have learnt respecting the courtship of fowls. I have
received long letters on this subject from Messrs. Hewitt and Tegetmeier,
and almost an essay from the late Mr. Brent. It will be admitted by every
one that these gentlemen, so well known from their published works, are
careful and experienced observers. They do not believe that the females
prefer certain males on account of the beauty of their plumage; but some
allowance must be made for the artificial state under which these birds
have long been kept. Mr. Tegetmeier is convinced that a gamecock, though
disfigured by being dubbed and with his hackles trimmed, would be accepted
as readily as a male retaining all his natural ornaments. Mr. Brent,
however, admits that the beauty of the male probably aids in exciting the
female; and her acquiescence is necessary. Mr. Hewitt is convinced that
the union is by no means left to mere chance, for the female almost
invariably prefers the most vigorous, defiant, and mettlesome male; hence
it is almost useless, as he remarks, "to attempt true breeding if a game-
cock in good health and condition runs the locality, for almost every hen
on leaving the roosting-place will resort to the game-cock, even though
that bird may not actually drive away the male of her own variety." Under
ordinary circumstances the males and females of the fowl seem to come to a
mutual understanding by means of certain gestures, described to me by Mr.
Brent. But hens will often avoid the officious attentions of young males.
Old hens, and hens of a pugnacious disposition, as the same writer informs
me, dislike strange males, and will not yield until well beaten into
compliance. Ferguson, however, describes how a quarrelsome hen was subdued
by the gentle courtship of a Shanghai cock. (21. 'Rare and Prize
Poultry,' 1854, p. 27.)
There is reason to believe that pigeons of both sexes prefer pairing with
birds of the same breed; and dovecot-pigeons dislike all the highly
improved breeds. (22. 'Variation of Animals and Plants under
Domestication,' vol. ii. p. 103.) Mr. Harrison Weir has lately heard from
a trustworthy observer, who keeps blue pigeons, that these drive away all
other coloured varieties, such as white, red, and yellow; and from another
observer, that a female dun carrier could not, after repeated trials, be
matched with a black male, but immediately paired with a dun. Again, Mr.
Tegetmeier had a female blue turbit that obstinately refused to pair with
two males of the same breed, which were successively shut up with her for
weeks; but on being let out she would have immediately accepted the first
blue dragon that offered. As she was a valuable bird, she was then shut up
for many weeks with a silver (i.e., very pale blue) male, and at last mated
with him. Nevertheless, as a general rule, colour appears to have little
influence on the pairing of pigeons. Mr. Tegetmeier, at my request,
stained some of his birds with magenta, but they were not much noticed by
the others.
Female pigeons occasionally feel a strong antipathy towards certain males,
without any assignable cause. Thus MM. Boitard and Corbie, whose
experience extended over forty-five years, state: "Quand une femelle
eprouve de l'antipathie pour un male avec lequel on veut l'accoupler,
malgre tous les feux de l'amour, malgre l'alpiste et le chenevis dont on la
nourrit pour augmenter son ardeur, malgre un emprisonnement de six mois et
meme d'un an, elle refuse constamment ses caresses; les avances empressees,
les agaceries, les tournoiemens, les tendres roucoulemens, rien ne peut lui
plaire ni l'emouvoir; gonflee, boudeuse, blottie dans un coin de sa prison,
elle n'en sort que pour boire et manger, ou pour repousser avec une espece
de rage des caresses devenues trop pressantes." (23. Boitard and Corbie,
'Les Pigeons,' etc., 1824, p. 12. Prosper Lucas ('Traite de l'Hered. Nat.'
tom. ii. 1850, p. 296) has himself observed nearly similar facts with
pigeons.) On the other hand, Mr. Harrison Weir has himself observed, and
has heard from several breeders, that a female pigeon will occasionally
take a strong fancy for a particular male, and will desert her own mate for
him. Some females, according to another experienced observer, Riedel (24.
Die Taubenzucht, 1824, s. 86.), are of a profligate disposition, and prefer
almost any stranger to their own mate. Some amorous males, called by our
English fanciers "gay birds," are so successful in their gallantries, that,
as Mr. H. Weir informs me, they must be shut up on account of the mischief
which they cause.
Wild turkeys in the United States, according to Audubon, "sometimes pay
their addresses to the domesticated females, and are generally received by
them with great pleasure." So that these females apparently prefer the
wild to their own males. (25. 'Ornithological Biography,' vol. i. p. 13.
See to the same effect, Dr. Bryant, in Allen's 'Mammals and Birds of
Florida,' p. 344.)
Here is a more curious case. Sir R. Heron during many years kept an
account of the habits of the peafowl, which he bred in large numbers. He
states that "the hens have frequently great preference to a particular
peafowl. They were all so fond of an old pied cock, that one year, when he
was confined, though still in view, they were constantly assembled close to
the trellice-walls of his prison, and would not suffer a japanned peacock
to touch them. On his being let out in the autumn, the oldest of the hens
instantly courted him and was successful in her courtship. The next year
he was shut up in a stable, and then the hens all courted his rival." (26.
'Proceedings, Zoological Society,' 1835, p. 54. The japanned peacock is
considered by Mr. Sclater as a distinct species, and has been named Pavo
nigripennis; but the evidence seems to me to show that it is only a
variety.) This rival was a japanned or black-winged peacock, to our eyes a
more beautiful bird than the common kind.
Lichtenstein, who was a good observer and had excellent opportunities of
observation at the Cape of Good Hope, assured Rudolphi that the female
widow-bird (Chera progne) disowns the male when robbed of the long tail-
feathers with which he is ornamented during the breeding-season. I presume
that this observation must have been made on birds under confinement. (27.
Rudolphi, 'Beitrage zur Anthropologie,' 1812, s. 184.) Here is an
analogous case; Dr. Jaeger (28. 'Die Darwin'sche Theorie, und ihre
Stellung zu Moral und Religion,' 1869, s. 59.), director of the Zoological
Gardens of Vienna, states that a male silver-pheasant, who had been
triumphant over all other males and was the accepted lover of the females,
had his ornamental plumage spoiled. He was then immediately superseded by
a rival, who got the upper hand and afterwards led the flock.
It is a remarkable fact, as shewing how important colour is in the
courtship of birds, that Mr. Boardman, a well-known collector and observer
of birds for many years in the Northern United States, has never in his
large experience seen an albino paired with another bird; yet he has had
opportunities of observing many albinos belonging to several species. (29.
This statement is given by Mr. A. Leith Adams, in his 'Field and Forest
Rambles,' 1873, p. 76, and accords with his own experience.) It can hardly
be maintained that albinos in a state of nature are incapable of breeding,
as they can be raised with the greatest facility under confinement. It
appears, therefore, that we must attribute the fact that they do not pair
to their rejection by their normally coloured comrades.
Female birds not only exert a choice, but in some few cases they court the
male, or even fight together for his possession. Sir R. Heron states that
with peafowl, the first advances are always made by the female; something
of the same kind takes place, according to Audubon, with the older females
of the wild turkey. With the capercailzie, the females flit round the male
whilst he is parading at one of the places of assemblage, and solicit his
attention. (30. In regard to peafowl, see Sir R. Heron, 'Proc. Zoolog.
Soc.' 1835, p. 54, and the Rev. E.S. Dixon, 'Ornamental Poultry,' 1848, p.
8. For the turkey, Audubon, ibid. p. 4. For the capercailzie, Lloyd,
'Game Birds of Sweden,' 1867, p. 23.) We have seen that a tame wild-duck
seduced an unwilling pintail drake after a long courtship. Mr. Bartlett
believes that the Lophophorus, like many other gallinaceous birds, is
naturally polygamous, but two females cannot be placed in the same cage
with a male, as they fight so much together. The following instance of
rivalry is more surprising as it relates to bullfinches, which usually pair
for life. Mr. Jenner Weir introduced a dull-coloured and ugly female into
his aviary, and she immediately attacked another mated female so
unmercifully that the latter had to be separated. The new female did all
the courtship, and was at last successful, for she paired with the male;
but after a time she met with a just retribution, for, ceasing to be
pugnacious, she was replaced by the old female, and the male then deserted
his new and returned to his old love.
In all ordinary cases the male is so eager that he will accept any female,
and does not, as far as we can judge, prefer one to the other; but, as we
shall hereafter see, exceptions to this rule apparently occur in some few
groups. With domesticated birds, I have heard of only one case of males
shewing any preference for certain females, namely, that of the domestic
cock, who, according to the high authority of Mr. Hewitt, prefers the
younger to the older hens. On the other hand, in effecting hybrid unions
between the male pheasant and common hens, Mr. Hewitt is convinced that the
pheasant invariably prefers the older birds. He does not appear to be in
the least influenced by their colour; but "is most capricious in his
attachments" (31. Mr. Hewitt, quoted in Tegetmeier's 'Poultry Book,' 1866,
p. 165.): from some inexplicable cause he shews the most determined
aversion to certain hens, which no care on the part of the breeder can
overcome. Mr. Hewitt informs me that some hens are quite unattractive even
to the males of their own species, so that they may be kept with several
cocks during a whole season, and not one egg out of forty or fifty will
prove fertile. On the other hand, with the long-tailed duck (Harelda
glacialis), "it has been remarked," says M. Ekstrom, "that certain females
are much more courted than the rest. Frequently, indeed, one sees an
individual surrounded by six or eight amorous males." Whether this
statement is credible, I know not; but the native sportsmen shoot these
females in order to stuff them as decoys. (32. Quoted in Lloyd's 'Game
Birds of Sweden,' p. 345.)
With respect to female birds feeling a preference for particular males, we
must bear in mind that we can judge of choice being exerted only by
analogy. If an inhabitant of another planet were to behold a number of
young rustics at a fair courting a pretty girl, and quarrelling about her
like birds at one of their places of assemblage, he would, by the eagerness
of the wooers to please her and to display their finery, infer that she had
the power of choice. Now with birds the evidence stands thus: they have
acute powers of observation, and they seem to have some taste for the
beautiful both in colour and sound. It is certain that the females
occasionally exhibit, from unknown causes, the strongest antipathies and
preferences for particular males. When the sexes differ in colour or in
other ornaments the males with rare exceptions are the more decorated,
either permanently or temporarily during the breeding-season. They
sedulously display their various ornaments, exert their voices, and perform
strange antics in the presence of the females. Even well-armed males, who,
it might be thought, would altogether depend for success on the law of
battle, are in most cases highly ornamented; and their ornaments have been
acquired at the expense of some loss of power. In other cases ornaments
have been acquired, at the cost of increased risk from birds and beasts of
prey. With various species many individuals of both sexes congregate at
the same spot, and their courtship is a prolonged affair. There is even
reason to suspect that the males and females within the same district do
not always succeed in pleasing each other and pairing.
What then are we to conclude from these facts and considerations? Does the
male parade his charms with so much pomp and rivalry for no purpose? Are
we not justified in believing that the female exerts a choice, and that she
receives the addresses of the male who pleases her most? It is not
probable that she consciously deliberates; but she is most excited or
attracted by the most beautiful, or melodious, or gallant males. Nor need
it be supposed that the female studies each stripe or spot of colour; that
the peahen, for instance, admires each detail in the gorgeous train of the
peacock--she is probably struck only by the general effect. Nevertheless,
after hearing how carefully the male Argus pheasant displays his elegant
primary wing-feathers, and erects his ocellated plumes in the right
position for their full effect; or again, how the male goldfinch
alternately displays his gold-bespangled wings, we ought not to feel too
sure that the female does not attend to each detail of beauty. We can
judge, as already remarked, of choice being exerted, only from analogy; and
the mental powers of birds do not differ fundamentally from ours. From
these various considerations we may conclude that the pairing of birds is
not left to chance; but that those males, which are best able by their
various charms to please or excite the female, are under ordinary
circumstances accepted. If this be admitted, there is not much difficulty
in understanding how male birds have gradually acquired their ornamental
characters. All animals present individual differences, and as man can
modify his domesticated birds by selecting the individuals which appear to
him the most beautiful, so the habitual or even occasional preference by
the female of the more attractive males would almost certainly lead to
their modification; and such modifications might in the course of time be
augmented to almost any extent, compatible with the existence of the
species.
VARIABILITY OF BIRDS, AND ESPECIALLY OF THEIR SECONDARY SEXUAL CHARACTERS.
Variability and inheritance are the foundations for the work of selection.
That domesticated birds have varied greatly, their variations being
inherited, is certain. That birds in a state of nature have been modified
into distinct races is now universally admitted. (33. According to Dr.
Blasius ('Ibis,' vol. ii. 1860, p. 297), there are 425 indubitable species
of birds which breed in Europe, besides sixty forms, which are frequently
regarded as distinct species. Of the latter, Blasius thinks that only ten
are really doubtful, and that the other fifty ought to be united with their
nearest allies; but this shews that there must be a considerable amount of
variation with some of our European birds. It is also an unsettled point
with naturalists, whether several North American birds ought to be ranked
as specifically distinct from the corresponding European species. So again
many North American forms which until lately were named as distinct
species, are now considered to be local races.) Variations may be divided
into two classes; those which appear to our ignorance to arise
spontaneously, and those which are directly related to the surrounding
conditions, so that all or nearly all the individuals of the same species
are similarly modified. Cases of the latter kind have recently been
observed with care by Mr. J.A. Allen (34. 'Mammals and Birds of East
Florida,' also an 'Ornithological Reconnaissance of Kansas,' etc.
Notwithstanding the influence of climate on the colours of birds, it is
difficult to account for the dull or dark tints of almost all the species
inhabiting certain countries, for instance, the Galapagos Islands under the
equator, the wide temperate plains of Patagonia, and, as it appears, Egypt
(see Mr. Hartshorne in the 'American Naturalist,' 1873, p. 747). These
countries are open, and afford little shelter to birds; but it seems
doubtful whether the absence of brightly coloured species can be explained
on the principle of protection, for on the Pampas, which are equally open,
though covered by green grass, and where the birds would be equally exposed
to danger, many brilliant and conspicuously coloured species are common. I
have sometimes speculated whether the prevailing dull tints of the scenery
in the above named countries may not have affected the appreciation of
bright colours by the birds inhabiting them.), who shews that in the United
States many species of birds gradually become more strongly coloured in
proceeding southward, and more lightly coloured in proceeding westward to
the arid plains of the interior. Both sexes seem generally to be affected
in a like manner, but sometimes one sex more than the other. This result
is not incompatible with the belief that the colours of birds are mainly
due to the accumulation of successive variations through sexual selection;
for even after the sexes have been greatly differentiated, climate might
produce an equal effect on both sexes, or a greater effect on one sex than
on the other, owing to some constitutional difference.
Individual differences between the members of the same species are admitted
by every one to occur under a state of nature. Sudden and strongly marked
variations are rare; it is also doubtful whether if beneficial they would
often be preserved through selection and transmitted to succeeding
generations. (35. 'Origin of Species' fifth edit. 1869, p.104. I had
always perceived, that rare and strongly-marked deviations of structure,
deserving to be called monstrosities, could seldom be preserved through
natural selection, and that the preservation of even highly-beneficial
variations would depend to a certain extent on chance. I had also fully
appreciated the importance of mere individual differences, and this led me
to insist so strongly on the importance of that unconscious form of
selection by man, which follows from the preservation of the most valued
individuals of each breed, without any intention on his part to modify the
characters of the breed. But until I read an able article in the 'North
British Review' (March 1867, p. 289, et seq.), which has been of more use
to me than any other Review, I did not see how great the chances were
against the preservation of variations, whether slight or strongly
pronounced, occurring only in single individuals.) Nevertheless, it may be
worth while to give the few cases which I have been able to collect,
relating chiefly to colour,--simple albinism and melanism being excluded.
Mr. Gould is well known to admit the existence of few varieties, for he
esteems very slight differences as specific; yet he states (36.
'Introduction to the Trochlidae,' p. 102.) that near Bogota certain
humming-birds belonging to the genus Cynanthus are divided into two or
three races or varieties, which differ from each other in the colouring of
the tail--"some having the whole of the feathers blue, while others have
the eight central ones tipped with beautiful green." It does not appear
that intermediate gradations have been observed in this or the following
cases. In the males alone of one of the Australian parrakeets "the thighs
in some are scarlet, in others grass-green." In another parrakeet of the
same country "some individuals have the band across the wing-coverts
bright-yellow, while in others the same part is tinged with red. (37.
Gould, 'Handbook to Birds of Australia,' vol. ii. pp. 32 and 68.) In the
United States some few of the males of the scarlet tanager (Tanagra rubra)
have "a beautiful transverse band of glowing red on the smaller wing-
coverts" (38. Audubon, 'Ornithological Biography,' 1838, vol. iv. p.
389.); but this variation seems to be somewhat rare, so that its
preservation through sexual selection would follow only under usually
favourable circumstances. In Bengal the Honey buzzard (Pernis cristata)
has either a small rudimental crest on its head, or none at all: so slight
a difference, however, would not have been worth notice, had not this same
species possessed in Southern India a well-marked occipital crest formed of
several graduated feathers." (39. Jerdon, 'Birds of India,' vol. i. p.
108; and Mr. Blyth, in 'Land and Water,' 1868, p. 381.)
The following case is in some respects more interesting. A pied variety of
the raven, with the head, breast, abdomen, and parts of the wings and tail-
feathers white, is confined to the Feroe Islands. It is not very rare
there, for Graba saw during his visit from eight to ten living specimens.
Although the characters of this variety are not quite constant, yet it has
been named by several distinguished ornithologists as a distinct species.
The fact of the pied birds being pursued and persecuted with much clamour
by the other ravens of the island was the chief cause which led Brunnich to
conclude that they were specifically distinct; but this is now known to be
an error. (40. Graba, 'Tagebuch Reise nach Faro,' 1830, ss. 51-54.
Macgillivray, 'History of British Birds,' vol. iii. p. 745, 'Ibis,' vol. v.
1863, p. 469.) This case seems analogous to that lately given of albino
birds not pairing from being rejected by their comrades.
In various parts of the northern seas a remarkable variety of the common
Guillemot (Uria troile) is found; and in Feroe, one out of every five
birds, according to Graba's estimation, presents this variation. It is
characterised (41. Graba, ibid. s. 54. Macgillivray, ibid. vol. v. p.
327.) by a pure white ring round the eye, with a curved narrow white line,
an inch and a half in length, extending back from the ring. This
conspicuous character has caused the bird to be ranked by several
ornithologists as a distinct species under the name of U. lacrymans, but it
is now known to be merely a variety. It often pairs with the common kind,
yet intermediate gradations have never been seen; nor is this surprising,
for variations which appear suddenly, are often, as I have elsewhere shewn
(42. 'Variation of Animals and Plants under Domestication,' vol. ii. p.
92.), transmitted either unaltered or not at all. We thus see that two
distinct forms of the same species may co-exist in the same district, and
we cannot doubt that if the one had possessed any advantage over the other,
it would soon have been multiplied to the exclusion of the latter. If, for
instance, the male pied ravens, instead of being persecuted by their
comrades, had been highly attractive (like the above pied peacock) to the
black female ravens their numbers would have rapidly increased. And this
would have been a case of sexual selection.
With respect to the slight individual differences which are common, in a
greater or less degree, to all the members of the same species, we have
every reason to believe that they are by far the most important for the
work of selection. Secondary sexual characters are eminently liable to
vary, both with animals in a state of nature and under domestication. (43.
On these points see also 'Variation of Animals and Plants under
Domestication,' vol. i. p. 253; vol ii. pp. 73, 75.) There is also reason
to believe, as we have seen in our eighth chapter, that variations are more
apt to occur in the male than in the female sex. All these contingencies
are highly favourable for sexual selection. Whether characters thus
acquired are transmitted to one sex or to both sexes, depends, as we shall
see in the following chapter, on the form of inheritance which prevails.
It is sometimes difficult to form an opinion whether certain slight
differences between the sexes of birds are simply the result of variability
with sexually-limited inheritance, without the aid of sexual selection, or
whether they have been augmented through this latter process. I do not
here refer to the many instances where the male displays splendid colours
or other ornaments, of which the female partakes to a slight degree; for
these are almost certainly due to characters primarily acquired by the male
having been more or less transferred to the female. But what are we to
conclude with respect to certain birds in which, for instance, the eyes
differ slightly in colour in the two sexes? (44. See, for instance, on
the irides of a Podica and Gallicrex in 'Ibis,' vol. ii. 1860, p. 206; and
vol. v. 1863, p. 426.) In some cases the eyes differ conspicuously; thus
with the storks of the genus Xenorhynchus, those of the male are blackish-
hazel, whilst those of the females are gamboge-yellow; with many hornbills
(Buceros), as I hear from Mr. Blyth (45. See also Jerdon, 'Birds of
India,' vol. i. pp. 243-245.), the males have intense crimson eyes, and
those of the females are white. In the Buceros bicornis, the hind margin
of the casque and a stripe on the crest of the beak are black in the male,
but not so in the female. Are we to suppose that these black marks and the
crimson colour of the eyes have been preserved or augmented through sexual
selection in the males? This is very doubtful; for Mr. Bartlett shewed me
in the Zoological Gardens that the inside of the mouth of this Buceros is
black in the male and flesh-coloured in the female; and their external
appearance or beauty would not be thus affected. I observed in Chile (46.
'Zoology of the Voyage of H.M.S. "Beagle,"' 1841, p. 6.) that the iris in
the condor, when about a year old, is dark-brown, but changes at maturity
into yellowish-brown in the male, and into bright red in the female. The
male has also a small, longitudinal, leaden-coloured, fleshy crest or comb.
The comb of many gallinaceous birds is highly ornamental, and assumes vivid
colours during the act of courtship; but what are we to think of the dull-
coloured comb of the condor, which does not appear to us in the least
ornamental? The same question may be asked in regard to various other
characters, such as the knob on the base of the beak of the Chinese goose
(Anser cygnoides), which is much larger in the male than in the female. No
certain answer can be given to these questions; but we ought to be cautious
in assuming that knobs and various fleshy appendages cannot be attractive
to the female, when we remember that with savage races of man various
hideous deformities--deep scars on the face with the flesh raised into
protuberances, the septum of the nose pierced by sticks or bones, holes in
the ears and lips stretched widely open--are all admired as ornamental.
Whether or not unimportant differences between the sexes, such as those
just specified, have been preserved through sexual selection, these
differences, as well as all others, must primarily depend on the laws of
variation. On the principle of correlated development, the plumage often
varies on different parts of the body, or over the whole body, in the same
manner. We see this well illustrated in certain breeds of the fowl. In
all the breeds the feathers on the neck and loins of the males are
elongated, and are called hackles; now when both sexes acquire a top-knot,
which is a new character in the genus, the feathers on the head of the male
become hackle-shaped, evidently on the principle of correlation; whilst
those on the head of the female are of the ordinary shape. The colour also
of the hackles forming the top-knot of the male, is often correlated with
that of the hackles on the neck and loins, as may be seen by comparing
these feathers in the golden and silver-spangled Polish, the Houdans, and
Creve-coeur breeds. In some natural species we may observe exactly the
same correlation in the colours of these same feathers, as in the males of
the splendid Gold and Amherst pheasants.
The structure of each individual feather generally causes any change in its
colouring to be symmetrical; we see this in the various laced, spangled,
and pencilled breeds of the fowl; and on the principle of correlation the
feathers over the whole body are often coloured in the same manner. We are
thus enabled without much trouble to rear breeds with their plumage marked
almost as symmetrically as in natural species. In laced and spangled fowls
the coloured margins of the feathers are abruptly defined; but in a mongrel
raised by me from a black Spanish cock glossed with green, and a white
game-hen, all the feathers were greenish-black, excepting towards their
extremities, which were yellowish-white; but between the white extremities
and the black bases, there was on each feather a symmetrical, curved zone
of dark-brown. In some instances the shaft of the feather determines the
distribution of the tints; thus with the body-feathers of a mongrel from
the same black Spanish cock and a silver-spangled Polish hen, the shaft,
together with a narrow space on each side, was greenish-black, and this was
surrounded by a regular zone of dark-brown, edged with brownish-white. In
these cases we have feathers symmetrically shaded, like those which give so
much elegance to the plumage of many natural species. I have also noticed
a variety of the common pigeon with the wing-bars symmetrically zoned with
three bright shades, instead of being simply black on a slaty-blue ground,
as in the parent-species.
In many groups of birds the plumage is differently coloured in the several
species, yet certain spots, marks, or stripes are retained by all.
Analogous cases occur with the breeds of the pigeon, which usually retain
the two wing-bars, though they may be coloured red, yellow, white, black,
or blue, the rest of the plumage being of some wholly different tint. Here
is a more curious case, in which certain marks are retained, though
coloured in a manner almost exactly the opposite of what is natural; the
aboriginal pigeon has a blue tail, with the terminal halves of the outer
webs of the two outer tail feathers white; now there is a sub-variety
having a white instead of a blue tail, with precisely that part black which
is white in the parent-species. (47. Bechstein, 'Naturgeschichte
Deutschlands,' B. iv. 1795, s. 31, on a sub-variety of the Monck pigeon.)
FORMATION AND VARIABILITY OF THE OCELLI OR EYE-LIKE SPOTS ON THE PLUMAGE OF
BIRDS.
[Fig. 53. Cyllo leda, Linn., from a drawing by Mr. Trimen, shewing the
extreme range of variation in the ocelli.
A. Specimen, from Mauritius, upper surface of fore-wing.
A1. Specimen, from Natal, ditto.
B. Specimen, from Java, upper surface of hind-wing.
B1. Specimen, from Mauritius, ditto.]
As no ornaments are more beautiful than the ocelli on the feathers of
various birds, on the hairy coats of some mammals, on the scales of
reptiles and fishes, on the skin of amphibians, on the wings of many
Lepidoptera and other insects, they deserve to be especially noticed. An
ocellus consists of a spot within a ring of another colour, like the pupil
within the iris, but the central spot is often surrounded by additional
concentric zones. The ocelli on the tail-coverts of the peacock offer a
familiar example, as well as those on the wings of the peacock-butterfly
(Vanessa). Mr. Trimen has given me a description of a S. African moth
(Gynanisa isis), allied to our Emperor moth, in which a magnificent ocellus
occupies nearly the whole surface of each hinder wing; it consists of a
black centre, including a semi-transparent crescent-shaped mark, surrounded
by successive, ochre-yellow, black, ochre-yellow, pink, white, pink, brown,
and whitish zones. Although we do not know the steps by which these
wonderfully beautiful and complex ornaments have been developed, the
process has probably been a simple one, at least with insects; for, as Mr.
Trimen writes to me, "no characters of mere marking or coloration are so
unstable in the Lepidoptera as the ocelli, both in number and size." Mr.
Wallace, who first called my attention to this subject, shewed me a series
of specimens of our common meadow-brown butterfly (Hipparchia janira)
exhibiting numerous gradations from a simple minute black spot to an
elegantly-shaded ocellus. In a S. African butterfly (Cyllo leda, Linn.),
belonging to the same family, the ocelli are even still more variable. In
some specimens (A, Fig. 53) large spaces on the upper surface of the wings
are coloured black, and include irregular white marks; and from this state
a complete gradation can be traced into a tolerably perfect ocellus (A1),
and this results from the contraction of the irregular blotches of colour.
In another series of specimens a gradation can be followed from excessively
minute white dots, surrounded by a scarcely visible black line (B), into
perfectly symmetrical and large ocelli (B1). (48. This woodcut has been
engraved from a beautiful drawing, most kindly made for me by Mr. Trimen;
see also his description of the wonderful amount of variation in the
coloration and shape of the wings of this butterfly, in his 'Rhopalocera
Africae Australis,' p. 186.) In cases like these, the development of a
perfect ocellus does not require a long course of variation and selection.
With birds and many other animals, it seems to follow from the comparison
of allied species that circular spots are often generated by the breaking
up and contraction of stripes. In the Tragopan pheasant faint white lines
in the female represent the beautiful white spots in the male (49. Jerdon,
'Birds of India,' vol. iii. p. 517.); and something of the same kind may be
observed in the two sexes of the Argus pheasant. However this may be,
appearances strongly favour the belief that on the one hand, a dark spot is
often formed by the colouring matter being drawn towards a central point
from a surrounding zone, which latter is thus rendered lighter; and, on the
other hand, that a white spot is often formed by the colour being driven
away from a central point, so that it accumulates in a surrounding darker
zone. In either case an ocellus is the result. The colouring matter seems
to be a nearly constant quantity, but is redistributed, either
centripetally or centrifugally. The feathers of the common guinea-fowl
offer a good instance of white spots surrounded by darker zones; and
wherever the white spots are large and stand near each other, the
surrounding dark zones become confluent. In the same wing-feather of the
Argus pheasant dark spots may be seen surrounded by a pale zone, and white
spots by a dark zone. Thus the formation of an ocellus in its most
elementary state appears to be a simple affair. By what further steps the
more complex ocelli, which are surrounded by many successive zones of
colour, have been generated, I will not pretend to say. But the zoned
feathers of the mongrels from differently coloured fowls, and the
extraordinary variability of the ocelli on many Lepidoptera, lead us to
conclude that their formation is not a complex process, but depends on some
slight and graduated change in the nature of the adjoining tissues.
GRADATION OF SECONDARY SEXUAL CHARACTERS.
[Fig. 54. Feather of Peacock, about two-thirds of natural size, drawn by
Mr. Ford. The transparent zone is represented by the outermost white zone,
confined to the upper end of the disc.]
Cases of gradation are important, as shewing us that highly complex
ornaments may be acquired by small successive steps. In order to discover
the actual steps by which the male of any existing bird has acquired his
magnificent colours or other ornaments, we ought to behold the long line of
his extinct progenitors; but this is obviously impossible. We may,
however, generally gain a clue by comparing all the species of the same
group, if it be a large one; for some of them will probably retain, at
least partially, traces of their former characters. Instead of entering on
tedious details respecting various groups, in which striking instances of
gradation could be given, it seems the best plan to take one or two
strongly marked cases, for instance that of the peacock, in order to see if
light can be thrown on the steps by which this bird bas become so
splendidly decorated. The peacock is chiefly remarkable from the
extraordinary length of his tail-coverts; the tail itself not being much
elongated. The barbs along nearly the whole length of these feathers stand
separate or are decomposed; but this is the case with the feathers of many
species, and with some varieties of the domestic fowl and pigeon. The
barbs coalesce towards the extremity of the shaft forming the oval disc or
ocellus, which is certainly one of the most beautiful objects in the world.
It consists of an iridescent, intensely blue, indented centre, surrounded
by a rich green zone, this by a broad coppery-brown zone, and this by five
other narrow zones of slightly different iridescent shades. A trifling
character in the disc deserves notice; the barbs, for a space along one of
the concentric zones are more or less destitute of their barbules, so that
a part of the disc is surrounded by an almost transparent zone, which gives
it a highly finished aspect. But I have elsewhere described (50.
'Variation of Animals and Plants under Domestication,' vol. i. p. 254.) an
exactly analogous variation in the hackles of a sub-variety of the game-
cock, in which the tips, having a metallic lustre, "are separated from the
lower part of the feather by a symmetrically shaped transparent zone,
composed of the naked portions of the barbs." The lower margin or base of
the dark-blue centre of the ocellus is deeply indented on the line of the
shaft. The surrounding zones likewise shew traces, as may be seen in the
drawing (Fig. 54), of indentations, or rather breaks. These indentations
are common to the Indian and Javan peacocks (Pavo cristatus and P.
muticus); and they seem to deserve particular attention, as probably
connected with the development of the ocellus; but for a long time I could
not conjecture their meaning.
If we admit the principle of gradual evolution, there must formerly have
existed many species which presented every successive step between the
wonderfully elongated tail-coverts of the peacock and the short tail-
coverts of all ordinary birds; and again between the magnificent ocelli of
the former, and the simpler ocelli or mere coloured spots on other birds;
and so with all the other characters of the peacock. Let us look to the
allied Gallinaceae for any still-existing gradations. The species and sub-
species of Polyplectron inhabit countries adjacent to the native land of
the peacock; and they so far resemble this bird that they are sometimes
called peacock-pheasants. I am also informed by Mr. Bartlett that they
resemble the peacock in their voice and in some of their habits. During
the spring the males, as previously described, strut about before the
comparatively plain-coloured females, expanding and erecting their tail and
wing-feathers, which are ornamented with numerous ocelli. I request the
reader to turn back to the drawing (Fig. 51) of a Polyplectron; In P.
napoleonis the ocelli are confined to the tail, and the back is of a rich
metallic blue; in which respects this species approaches the Java peacock.
P. hardwickii possesses a peculiar top-knot, which is also somewhat like
that of the Java peacock. In all the species the ocelli on the wings and
tail are either circular or oval, and consist of a beautiful, iridescent,
greenish-blue or greenish-purple disc, with a black border. This border in
P. chinquis shades into brown, edged with cream colour, so that the ocellus
is here surrounded with variously shaded, though not bright, concentric
zones. The unusual length of the tail-coverts is another remarkable
character in Polyplectron; for in some of the species they are half, and in
others two-thirds as long as the true tail-feathers. The tail-coverts are
ocellated as in the peacock. Thus the several species of Polyplectron
manifestly make a graduated approach to the peacock in the length of their
tail-coverts, in the zoning of the ocelli, and in some other characters.
[Fig. 55. Part of a tail-covert of Polyplectron chinquis, with the two
ocelli of natural size.
Fig. 56. Part of a tail-covert of Polyplectron malaccense, with the two
ocelli, partially confluent, of natural size.]
Notwithstanding this approach, the first species of Polyplectron which I
examined almost made me give up the search; for I found not only that the
true tail-feathers, which in the peacock are quite plain, were ornamented
with ocelli, but that the ocelli on all the feathers differed fundamentally
from those of the peacock, in there being two on the same feather (Fig.
55), one on each side of the shaft. Hence I concluded that the early
progenitors of the peacock could not have resembled a Polyplectron. But on
continuing my search, I observed that in some of the species the two ocelli
stood very near each other; that in the tail-feathers of P. hardwickii they
touched each other; and, finally, that on the tail-coverts of this same
species as well as of P. malaccense (Fig. 56) they were actually confluent.
As the central part alone is confluent, an indentation is left at both the
upper and lower ends; and the surrounding coloured zones are likewise
indented. A single ocellus is thus formed on each tail-covert, though
still plainly betraying its double origin. These confluent ocelli differ
from the single ocelli of the peacock in having an indentation at both
ends, instead of only at the lower or basal end. The explanation, however,
of this difference is not difficult; in some species of Polyplectron the
two oval ocelli on the same feather stand parallel to each other; in other
species (as in P. chinquis) they converge towards one end; now the partial
confluence of two convergent ocelli would manifestly leave a much deeper
indentation at the divergent than at the convergent end. It is also
manifest that if the convergence were strongly pronounced and the
confluence complete, the indentation at the convergent end would tend to
disappear.
The tail-feathers in both species of the peacock are entirely destitute of
ocelli, and this apparently is related to their being covered up and
concealed by the long tail-coverts. In this respect they differ remarkably
from the tail-feathers of Polyplectron, which in most of the species are
ornamented with larger ocelli than those on the tail-coverts. Hence I was
led carefully to examine the tail-feathers of the several species, in order
to discover whether their ocelli shewed any tendency to disappear; and to
my great satisfaction, this appeared to be so. The central tail-feathers
of P. napoleonis have the two ocelli on each side of the shaft perfectly
developed; but the inner ocellus becomes less and less conspicuous on the
more exterior tail-feathers, until a mere shadow or rudiment is left on the
inner side of the outermost feather. Again, in P. malaccense, the ocelli
on the tail-coverts are, as we have seen, confluent; and these feathers are
of unusual length, being two-thirds of the length of the tail-feathers, so
that in both these respects they approach the tail-coverts of the peacock.
Now in P. malaccense, the two central tail-feathers alone are ornamented,
each with two brightly-coloured ocelli, the inner ocellus having completely
disappeared from all the other tail-feathers. Consequently the tail-
coverts and tail-feathers of this species of Polyplectron make a near
approach in structure and ornamentation to the corresponding feathers of
the peacock.
As far, then, as gradation throws light on the steps by which the
magnificent train of the peacock has been acquired, hardly anything more is
needed. If we picture to ourselves a progenitor of the peacock in an
almost exactly intermediate condition between the existing peacock, with
his enormously elongated tail-coverts, ornamented with single ocelli, and
an ordinary gallinaceous bird with short tail-coverts, merely spotted with
some colour, we shall see a bird allied to Polyplectron--that is, with
tail-coverts, capable of erection and expansion, ornamented with two
partially confluent ocelli, and long enough almost to conceal the tail-
feathers, the latter having already partially lost their ocelli. The
indentation of the central disc and of the surrounding zones of the
ocellus, in both species of peacock, speaks plainly in favour of this view,
and is otherwise inexplicable. The males of Polyplectron are no doubt
beautiful birds, but their beauty, when viewed from a little distance,
cannot be compared with that of the peacock. Many female progenitors of
the peacock must, during a long line of descent, have appreciated this
superiority; for they have unconsciously, by the continued preference for
the most beautiful males, rendered the peacock the most splendid of living
birds.
ARGUS PHEASANT.
Another excellent case for investigation is offered by the ocelli on the
wing-feathers of the Argus pheasant, which are shaded in so wonderful a
manner as to resemble balls lying loose within sockets, and consequently
differ from ordinary ocelli. No one, I presume, will attribute the
shading, which has excited the admiration of many experienced artists, to
chance--to the fortuitous concourse of atoms of colouring matter. That
these ornaments should have been formed through the selection of many
successive variations, not one of which was originally intended to produce
the ball-and-socket effect, seems as incredible as that one of Raphael's
Madonnas should have been formed by the selection of chance daubs of paint
made by a long succession of young artists, not one of whom intended at
first to draw the human figure. In order to discover how the ocelli have
been developed, we cannot look to a long line of progenitors, nor to many
closely-allied forms, for such do not now exist. But fortunately the
several feathers on the wing suffice to give us a clue to the problem, and
they prove to demonstration that a gradation is at least possible from a
mere spot to a finished ball-and-socket ocellus.
[Fig. 57. Part of secondary wing-feather of Argus pheasant, shewing two
perfect ocelli, a and b. A, B, C, D, etc., are dark stripes running
obliquely down, each to an ocellus.
[Much of the web on both sides, especially to the left of the shaft, has
been cut off.]
Fig.59. Portion of one of the secondary wing-feathers near to the body,
shewing the so-called elliptic ornaments. The right-hand figure is given
merely as a diagram for the sake of the letters of reference.
A, B, C, D, etc. Rows of spots running down to and forming the elliptic
ornaments.
b. Lowest spot or mark in row B.
c. The next succeeding spot or mark in the same row.
d. Apparently a broken prolongation of the spot c. in the same row B.]
The wing-feathers, bearing the ocelli, are covered with dark stripes (Fig.
57) or with rows of dark spots (Fig. 59), each stripe or row of spots
running obliquely down the outer side of the shaft to one of the ocelli.
The spots are generally elongated in a line transverse to the row in which
they stand. They often become confluent either in the line of the row--and
then they form a longitudinal stripe--or transversely, that is, with the
spots in the adjoining rows, and then they form transverse stripes. A spot
sometimes breaks up into smaller spots, which still stand in their proper
places.
It will be convenient first to describe a perfect ball-and-socket ocellus.
This consists of an intensely black circular ring, surrounding a space
shaded so as exactly to resemble a ball. The figure here given has been
admirably drawn by Mr. Ford and well engraved, but a woodcut cannot exhibit
the exquisite shading of the original. The ring is almost always slightly
broken or interrupted (Fig. 57) at a point in the upper half, a little to
the right of and above the white shade on the enclosed ball; it is also
sometimes broken towards the base on the right hand. These little breaks
have an important meaning. The ring is always much thickened, with the
edges ill-defined towards the left-hand upper corner, the feather being
held erect, in the position in which it is here drawn. Beneath this
thickened part there is on the surface of the ball an oblique almost pure-
white mark, which shades off downwards into a pale-leaden hue, and this
into yellowish and brown tints, which insensibly become darker and darker
towards the lower part of the ball. It is this shading which gives so
admirably the effect of light shining on a convex surface. If one of the
balls be examined, it will be seen that the lower part is of a brown tint
and is indistinctly separated by a curved oblique line from the upper part,
which is yellower and more leaden; this curved oblique line runs at right
angles to the longer axis of the white patch of light, and indeed of all
the shading; but this difference in colour, which cannot of course be shewn
in the woodcut, does not in the least interfere with the perfect shading of
the ball. It should be particularly observed that each ocellus stands in
obvious connection either with a dark stripe, or with a longitudinal row of
dark spots, for both occur indifferently on the same feather. Thus in Fig.
57 stripe A runs to ocellus a; B runs to ocellus b; stripe C is broken in
the upper part, and runs down to the next succeeding ocellus, not
represented in the woodcut; D to the next lower one, and so with the
stripes E and F. Lastly, the several ocelli are separated from each other
by a pale surface bearing irregular black marks.
[Fig. 58. Basal part of the secondary wing feather, nearest to the body.]
I will next describe the other extreme of the series, namely, the first
trace of an ocellus. The short secondary wing-feather (Fig. 58), nearest
to the body, is marked like the other feathers, with oblique, longitudinal,
rather irregular, rows of very dark spots. The basal spot, or that nearest
the shaft, in the five lower rows (excluding the lowest one) is a little
larger than the other spots of the same row, and a little more elongated in
a transverse direction. It differs also from the other spots by being
bordered on its upper side with some dull fulvous shading. But this spot
is not in any way more remarkable than those on the plumage of many birds,
and might easily be overlooked. The next higher spot does not differ at
all from the upper ones in the same row. The larger basal spots occupy
exactly the same relative position on these feathers as do the perfect
ocelli on the longer wing-feathers.
By looking to the next two or three succeeding wing-feathers, an absolutely
insensible gradation can be traced from one of the last-described basal
spots, together with the next higher one in the same row, to a curious
ornament, which cannot be called an ocellus, and which I will name, from
the want of a better term, an "elliptic ornament." These are shewn in the
accompanying figure (Fig. 59). We here see several oblique rows, A, B, C,
D, etc. (see the lettered diagram on the right hand), of dark spots of the
usual character. Each row of spots runs down to and is connected with one
of the elliptic ornaments, in exactly the same manner as each stripe in
Fig. 57 runs down to and is connected with one of the ball-and-socket
ocelli. Looking to any one row, for instance, B, in Fig. 59, the lowest
mark (b) is thicker and considerably longer than the upper spots, and has
its left extremity pointed and curved upwards. This black mark is abruptly
bordered on its upper side by a rather broad space of richly shaded tints,
beginning with a narrow brown zone, which passes into orange, and this into
a pale leaden tint, with the end towards the shaft much paler. These
shaded tints together fill up the whole inner space of the elliptic
ornament. The mark (b) corresponds in every respect with the basal shaded
spot of the simple feather described in the last paragraph (Fig. 58), but
is more highly developed and more brightly coloured. Above and to the
right of this spot (b, Fig. 59), with its bright shading, there is a long
narrow, black mark (c), belonging to the same row, and which is arched a
little downwards so as to face (b). This mark is sometimes broken into two
portions. It is also narrowly edged on the lower side with a fulvous tint.
To the left of and above c, in the same oblique direction, but always more
or less distinct from it, there is another black mark (d). This mark is
generally sub-triangular and irregular in shape, but in the one lettered in
the diagram it is unusually narrow, elongated, and regular. It apparently
consists of a lateral and broken prolongation of the mark (c), together
with its confluence with a broken and prolonged part of the next spot
above; but I do not feel sure of this. These three marks, b, c, and d,
with the intervening bright shades, form together the so-called elliptic
ornament. These ornaments placed parallel to the shaft, manifestly
correspond in position with the ball-and-socket ocelli. Their extremely
elegant appearance cannot be appreciated in the drawing, as the orange and
leaden tints, contrasting so well with the black marks, cannot be shewn.
[Fig. 60. An ocellus in an intermediate condition between the elliptic
ornament and the perfect ball-and-socket ocellus.]
Between one of the elliptic ornaments and a perfect ball-and-socket
ocellus, the gradation is so perfect that it is scarcely possible to decide
when the latter term ought to be used. The passage from the one into the
other is effected by the elongation and greater curvature in opposite
directions of the lower black mark (b, Fig. 59), and more especially of the
upper one (c), together with the contraction of the elongated sub-
triangular or narrow mark (d), so that at last these three marks become
confluent, forming an irregular elliptic ring. This ring is gradually
rendered more and more circular and regular, increasing at the same time in
diameter. I have here given a drawing (Fig. 60) of the natural size of an
ocellus not as yet quite perfect. The lower part of the black ring is much
more curved than is the lower mark in the elliptic ornament (b, Fig. 59).
The upper part of the ring consists of two or three separate portions; and
there is only a trace of the thickening of the portion which forms the
black mark above the white shade. This white shade itself is not as yet
much concentrated; and beneath it the surface is brighter coloured than in
a perfect ball-and-socket ocellus. Even in the most perfect ocelli traces
of the junction of three or four elongated black marks, by which the ring
has been formed, may often be detected. The irregular sub-triangular or
narrow mark (d, Fig. 59), manifestly forms, by its contraction and
equalisation, the thickened portion of the ring above the white shade on a
perfect ball-and-socket ocellus. The lower part of the ring is invariably
a little thicker than the other parts (Fig. 57), and this follows from the
lower black mark of the elliptic ornament (b, Fig. 59) having originally
been thicker than the upper mark (c). Every step can be followed in the
process of confluence and modification; and the black ring which surrounds
the ball of the ocellus is unquestionably formed by the union and
modification of the three black marks, b, c, d, of the elliptic ornament.
The irregular zigzag black marks between the successive ocelli (Fig. 57)
are plainly due to the breaking up of the somewhat more regular but similar
marks between the elliptic ornaments.
The successive steps in the shading of the ball-and-socket ocelli can be
followed out with equal clearness. The brown, orange, and pale-leadened
narrow zones, which border the lower black mark of the elliptic ornament,
can be seen gradually to become more and more softened and shaded into each
other, with the upper lighter part towards the left-hand corner rendered
still lighter, so as to become almost white, and at the same time more
contracted. But even in the most perfect ball-and-socket ocelli a slight
difference in the tints, though not in the shading, between the upper and
lower parts of the ball can be perceived, as before noticed; and the line
of separation is oblique, in the same direction as the bright coloured
shades of the elliptic ornaments. Thus almost every minute detail in the
shape and colouring of the ball-and-socket ocelli can be shewn to follow
from gradual changes in the elliptic ornaments; and the development of the
latter can be traced by equally small steps from the union of two almost
simple spots, the lower one (Fig. 58) having some dull fulvous shading on
its upper side.
[Fig. 61. Portion near summit of one of the secondary wing-feathers,
bearing perfect ball-and-socket ocelli.
a. Ornamented upper part.
b. Uppermost, imperfect ball-and-socket ocellus. (The shading above the
white mark on the summit of the ocellus is here a little too dark.)
c. Perfect ocellus.]
The extremities of the longer secondary feathers which bear the perfect
ball-and-socket ocelli, are peculiarly ornamented (Fig. 61). The oblique
longitudinal stripes suddenly cease upwards and become confused; and above
this limit the whole upper end of the feather (a) is covered with white
dots, surrounded by little black rings, standing on a dark ground. The
oblique stripe belonging to the uppermost ocellus (b) is barely represented
by a very short irregular black mark with the usual, curved, transverse
base. As this stripe is thus abruptly cut off, we can perhaps understand
from what has gone before, how it is that the upper thickened part of the
ring is here absent; for, as before stated, this thickened part apparently
stands in some relation with a broken prolongation from the next higher
spot. From the absence of the upper and thickened part of the ring, the
uppermost ocellus, though perfect in all other respects, appears as if its
top had been obliquely sliced off. It would, I think, perplex any one, who
believes that the plumage of the Argus pheasant was created as we now see
it, to account for the imperfect condition of the uppermost ocellus. I
should add that on the secondary wing-feather farthest from the body all
the ocelli are smaller and less perfect than on the other feathers, and
have the upper part of the ring deficient, as in the case just mentioned.
The imperfection here seems to be connected with the fact that the spots on
this feather shew less tendency than usual to become confluent into
stripes; they are, on the contrary, often broken up into smaller spots, so
that two or three rows run down to the same ocellus.
There still remains another very curious point, first observed by Mr. T.W.
Wood (51. The 'Field,' May 28, 1870.), which deserves attention. In a
photograph, given me by Mr. Ward, of a specimen mounted as in the act of
display, it may be seen that on the feathers which are held
perpendicularly, the white marks on the ocelli, representing light
reflected from a convex surface, are at the upper or further end, that is,
are directed upwards; and the bird whilst displaying himself on the ground
would naturally be illuminated from above. But here comes the curious
point; the outer feathers are held almost horizontally, and their ocelli
ought likewise to appear as if illuminated from above, and consequently the
white marks ought to be placed on the upper sides of the ocelli; and,
wonderful as is the fact, they are thus placed! Hence the ocelli on the
several feathers, though occupying very different positions with respect to
the light, all appear as if illuminated from above, just as an artist would
have shaded them. Nevertheless they are not illuminated from strictly the
same point as they ought to be; for the white marks on the ocelli of the
feathers which are held almost horizontally, are placed rather too much
towards the further end; that is, they are not sufficiently lateral. We
have, however, no right to expect absolute perfection in a part rendered
ornamental through sexual selection, any more than we have in a part
modified through natural selection for real use; for instance, in that
wondrous organ the human eye. And we know what Helmholtz, the highest
authority in Europe on the subject, has said about the human eye; that if
an optician had sold him an instrument so carelessly made, he would have
thought himself fully justified in returning it. (52. 'Popular Lectures
on Scientific Subjects,' Eng. trans. 1873, pp. 219, 227, 269, 390.)
We have now seen that a perfect series can be followed, from simple spots
to the wonderful ball-and-socket ornaments. Mr. Gould, who kindly gave me
some of these feathers, fully agrees with me in the completeness of the
gradation. It is obvious that the stages in development exhibited by the
feathers on the same bird do not at all necessarily shew us the steps
passed through by the extinct progenitors of the species; but they probably
give us the clue to the actual steps, and they at least prove to
demonstration that a gradation is possible. Bearing in mind how carefully
the male Argus pheasant displays his plumes before the female, as well as
the many facts rendering it probable that female birds prefer the more
attractive males, no one who admits the agency of sexual selection in any
case will deny that a simple dark spot with some fulvous shading might be
converted, through the approximation and modification of two adjoining
spots, together with some slight increase of colour, into one of the so-
called elliptic ornaments. These latter ornaments have been shewn to many
persons, and all have admitted that they are beautiful, some thinking them
even more so than the ball-and-socket ocelli. As the secondary plumes
became lengthened through sexual selection, and as the elliptic ornaments
increased in diameter, their colours apparently became less bright; and
then the ornamentation of the plumes had to be gained by an improvement in
the pattern and shading; and this process was carried on until the
wonderful ball-and-socket ocelli were finally developed. Thus we can
understand--and in no other way as it seems to me--the present condition
and origin of the ornaments on the wing-feathers of the Argus pheasant.
From the light afforded by the principle of gradation--from what we know of
the laws of variation--from the changes which have taken place in many of
our domesticated birds--and, lastly, from the character (as we shall
hereafter see more clearly) of the immature plumage of young birds--we can
sometimes indicate, with a certain amount of confidence, the probable steps
by which the males have acquired their brilliant plumage and various
ornaments; yet in many cases we are involved in complete darkness. Mr.
Gould several years ago pointed out to me a humming-bird, the Urosticte
benjamini, remarkable for the curious differences between the sexes. The
male, besides a splendid gorget, has greenish-black tail-feathers, with the
four CENTRAL ones tipped with white; in the female, as with most of the
allied species, the three OUTER tail-feathers on each side are tipped with
white, so that the male has the four central, whilst the female has the six
exterior feathers ornamented with white tips. What makes the case more
curious is that, although the colouring of the tail differs remarkably in
both sexes of many kinds of humming-birds, Mr. Gould does not know a single
species, besides the Urosticte, in which the male has the four central
feathers tipped with white.
The Duke of Argyll, in commenting on this case (53. 'The Reign of Law,'
1867, p. 247.), passes over sexual selection, and asks, "What explanation
does the law of natural selection give of such specific varieties as
these?" He answers "none whatever"; and I quite agree with him. But can
this be so confidently said of sexual selection? Seeing in how many ways
the tail-feathers of humming-birds differ, why should not the four central
feathers have varied in this one species alone, so as to have acquired
white tips? The variations may have been gradual, or somewhat abrupt as in
the case recently given of the humming-birds near Bogota, in which certain
individuals alone have the "central tail-feathers tipped with beautiful
green." In the female of the Urosticte I noticed extremely minute or
rudimental white tips to the two outer of the four central black tail-
feathers; so that here we have an indication of change of some kind in the
plumage of this species. If we grant the possibility of the central tail-
feathers of the male varying in whiteness, there is nothing strange in such
variations having been sexually selected. The white tips, together with
the small white ear-tufts, certainly add, as the Duke of Argyll admits, to
the beauty of the male; and whiteness is apparently appreciated by other
birds, as may be inferred from such cases as the snow-white male of the
Bell-bird. The statement made by Sir R. Heron should not be forgotten,
namely, that his peahens, when debarred from access to the pied peacock,
would not unite with any other male, and during that season produced no
offspring. Nor is it strange that variations in the tail-feathers of the
Urosticte should have been specially selected for the sake of ornament, for
the next succeeding genus in the family takes its name of Metallura from
the splendour of these feathers. We have, moreover, good evidence that
humming-birds take especial pains in displaying their tail-feathers; Mr.
Belt (54. 'The Naturalist in Nicaragua,' 1874, p. 112.), after describing
the beauty of the Florisuga mellivora, says, "I have seen the female
sitting on a branch, and two males displaying their charms in front of her.
One would shoot up like a rocket, then suddenly expanding the snow-white
tail, like an inverted parachute, slowly descend in front of her, turning
round gradually to shew off back and front...The expanded white tail
covered more space than all the rest of the bird, and was evidently the
grand feature in the performance. Whilst one male was descending, the
other would shoot up and come slowly down expanded. The entertainment
would end in a fight between the two performers; but whether the most
beautiful or the most pugnacious was the accepted suitor, I know not." Mr.
Gould, after describing the peculiar plumage of the Urosticte, adds, "that
ornament and variety is the sole object, I have myself but little doubt."
(55. 'Introduction to the Trochilidae,' 1861, p. 110.) If this be
admitted, we can perceive that the males which during former times were
decked in the most elegant and novel manner would have gained an advantage,
not in the ordinary struggle for life, but in rivalry with other males, and
would have left a larger number of offspring to inherit their newly-
acquired beauty.
CHAPTER XV.
Birds--continued.
Discussion as to why the males alone of some species, and both sexes of
others, are brightly coloured--On sexually-limited inheritance, as applied
to various structures and to brightly-coloured plumage--Nidification in
relation to colour--Loss of nuptial plumage during the winter.
We have in this chapter to consider why the females of many birds have not
acquired the same ornaments as the male; and why, on the other hand, both
sexes of many other birds are equally, or almost equally, ornamented? In
the following chapter we shall consider the few cases in which the female
is more conspicuously coloured than the male.
In my 'Origin of Species' (1. Fourth edition, 1866, p. 241.) I briefly
suggested that the long tail of the peacock would be inconvenient and the
conspicuous black colour of the male capercailzie dangerous, to the female
during the period of incubation: and consequently that the transmission of
these characters from the male to the female offspring had been checked
through natural selection. I still think that this may have occurred in
some few instances: but after mature reflection on all the facts which I
have been able to collect, I am now inclined to believe that when the sexes
differ, the successive variations have generally been from the first
limited in their transmission to the same sex in which they first arose.
Since my remarks appeared, the subject of sexual coloration has been
discussed in some very interesting papers by Mr. Wallace (2. 'Westminster
Review,' July 1867. 'Journal of Travel,' vol. i. 1868, p. 73.), who
believes that in almost all cases the successive variations tended at first
to be transmitted equally to both sexes; but that the female was saved,
through natural selection, from acquiring the conspicuous colours of the
male, owing to the danger which she would thus have incurred during
incubation.
This view necessitates a tedious discussion on a difficult point, namely,
whether the transmission of a character, which is at first inherited by
both sexes can be subsequently limited in its transmission to one sex alone
by means of natural selection. We must bear in mind, as shewn in the
preliminary chapter on sexual selection, that characters which are limited
in their development to one sex are always latent in the other. An
imaginary illustration will best aid us in seeing the difficulty of the
case; we may suppose that a fancier wished to make a breed of pigeons, in
which the males alone should be coloured of a pale blue, whilst the females
retained their former slaty tint. As with pigeons characters of all kinds
are usually transmitted to both sexes equally, the fancier would have to
try to convert this latter form of inheritance into sexually-limited
transmission. All that he could do would be to persevere in selecting
every male pigeon which was in the least degree of a paler blue; and the
natural result of this process, if steadily carried on for a long time, and
if the pale variations were strongly inherited or often recurred, would be
to make his whole stock of a lighter blue. But our fancier would be
compelled to match, generation after generation, his pale blue males with
slaty females, for he wishes to keep the latter of this colour. The result
would generally be the production either of a mongrel piebald lot, or more
probably the speedy and complete loss of the pale-blue tint; for the
primordial slaty colour would be transmitted with prepotent force.
Supposing, however, that some pale-blue males and slaty females were
produced during each successive generation, and were always crossed
together, then the slaty females would have, if I may use the expression,
much blue blood in their veins, for their fathers, grandfathers, etc., will
all have been blue birds. Under these circumstances it is conceivable
(though I know of no distinct facts rendering it probable) that the slaty
females might acquire so strong a latent tendency to pale-blueness, that
they would not destroy this colour in their male offspring, their female
offspring still inheriting the slaty tint. If so, the desired end of
making a breed with the two sexes permanently different in colour might be
gained.
The extreme importance, or rather necessity in the above case of the
desired character, namely, pale-blueness, being present though in a latent
state in the female, so that the male offspring should not be deteriorated,
will be best appreciated as follows: the male of Soemmerring's pheasant
has a tail thirty-seven inches in length, whilst that of the female is only
eight inches; the tail of the male common pheasant is about twenty inches,
and that of the female twelve inches long. Now if the female Soemmerring
pheasant with her SHORT tail were crossed with the male common pheasant,
there can be no doubt that the male hybrid offspring would have a much
LONGER tail than that of the pure offspring of the common pheasant. On the
other hand, if the female common pheasant, with a tail much longer than
that of the female Soemmerring pheasant, were crossed with the male of the
latter, the male hybrid offspring would have a much SHORTER tail than that
of the pure offspring of Soemmerring's pheasant. (3. Temminck says that
the tail of the female Phasianus Soemmerringii is only six inches long,
'Planches coloriees,' vol. v. 1838, pp. 487 and 488: the measurements
above given were made for me by Mr. Sclater. For the common pheasant, see
Macgillivray, 'History of British Birds,' vol. i. pp. 118-121.)
Our fancier, in order to make his new breed with the males of a pale-blue
tint, and the females unchanged, would have to continue selecting the males
during many generations; and each stage of paleness would have to be fixed
in the males, and rendered latent in the females. The task would be an
extremely difficult one, and has never been tried, but might possibly be
successfully carried out. The chief obstacle would be the early and
complete loss of the pale-blue tint, from the necessity of reiterated
crosses with the slaty female, the latter not having at first any LATENT
tendency to produce pale-blue offspring.
On the other hand, if one or two males were to vary ever so slightly in
paleness, and the variations were from the first limited in their
transmission to the male sex, the task of making a new breed of the desired
kind would be easy, for such males would simply have to be selected and
matched with ordinary females. An analogous case has actually occurred,
for there are breeds of the pigeon in Belgium (4. Dr. Chapuis, 'Le Pigeon
Voyageur Belge,' 1865, p. 87.) in which the males alone are marked with
black striae. So again Mr. Tegetmeier has recently shewn (5. The 'Field,'
Sept. 1872.) that dragons not rarely produce silver-coloured birds, which
are almost always hens; and he himself has bred ten such females. It is on
the other hand a very unusual event when a silver male is produced; so that
nothing would be easier, if desired, than to make a breed of dragons with
blue males and silver females. This tendency is indeed so strong that when
Mr. Tegetmeier at last got a silver male and matched him with one of the
silver females, he expected to get a breed with both sexes thus coloured;
he was however disappointed, for the young male reverted to the blue colour
of his grandfather, the young female alone being silver. No doubt with
patience this tendency to reversion in the males, reared from an occasional
silver male matched with a silver hen, might be eliminated, and then both
sexes would be coloured alike; and this very process has been followed with
success by Mr. Esquilant in the case of silver turbits.
With fowls, variations of colour, limited in their transmission to the male
sex, habitually occur. When this form of inheritance prevails, it might
well happen that some of the successive variations would be transferred to
the female, who would then slightly resemble the male, as actually occurs
in some breeds. Or again, the greater number, but not all, of the
successive steps might be transferred to both sexes, and the female would
then closely resemble the male. There can hardly be a doubt that this is
the cause of the male pouter pigeon having a somewhat larger crop, and of
the male carrier pigeon having somewhat larger wattles, than their
respective females; for fanciers have not selected one sex more than the
other, and have had no wish that these characters should be more strongly
displayed in the male than in the female, yet this is the case with both
breeds.
The same process would have to be followed, and the same difficulties
encountered, if it were desired to make a breed with the females alone of
some new colour.
Lastly, our fancier might wish to make a breed with the two sexes differing
from each other, and both from the parent species. Here the difficulty
would be extreme, unless the successive variations were from the first
sexually limited on both sides, and then there would be no difficulty. We
see this with the fowl; thus the two sexes of the pencilled Hamburghs
differ greatly from each other, and from the two sexes of the aboriginal
Gallus bankiva; and both are now kept constant to their standard of
excellence by continued selection, which would be impossible unless the
distinctive characters of both were limited in their transmission.
The Spanish fowl offers a more curious case; the male has an immense comb,
but some of the successive variations, by the accumulation of which it was
acquired, appear to have been transferred to the female; for she has a comb
many times larger than that of the females of the parent species. But the
comb of the female differs in one respect from that of the male, for it is
apt to lop over; and within a recent period it has been ordered by the
fancy that this should always be the case, and success has quickly followed
the order. Now the lopping of the comb must be sexually limited in its
transmission, otherwise it would prevent the comb of the male from being
perfectly upright, which would be abhorrent to every fancier. On the other
hand, the uprightness of the comb in the male must likewise be a sexually-
limited character, otherwise it would prevent the comb of the female from
lopping over.
From the foregoing illustrations, we see that even with almost unlimited
time at command, it would be an extremely difficult and complex, perhaps an
impossible process, to change one form of transmission into the other
through selection. Therefore, without distinct evidence in each case, I am
unwilling to admit that this has been effected in natural species. On the
other hand, by means of successive variations, which were from the first
sexually limited in their transmission, there would not be the least
difficulty in rendering a male bird widely different in colour or in any
other character from the female; the latter being left unaltered, or
slightly altered, or specially modified for the sake of protection.
As bright colours are of service to the males in their rivalry with other
males, such colours would be selected whether or not they were transmitted
exclusively to the same sex. Consequently the females might be expected
often to partake of the brightness of the males to a greater or less
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