WE must now consider the transmission
of characters, as limited by
age, in reference to sexual selection.
The truth and importance of the
principle of inheritance at corresponding
ages need not here be discussed,
as enough has already been said
on the subject. Before giving
the several rather complex rules
or classes of cases, under which
the differences in plumage between
the young and the old, as far
as known to me, may be included,
it will be well to make a few
preliminary remarks.
With animals of all kinds when
the adults differ in colour from
the young, and the colours of
the latter are not, as far as
we can see, of any special service,
they may generally be attributed,
like various embryological structures,
to the retention of a former
character. But this view can
be maintained with confidence,
only when the young of several
species resemble each other closely,
and likewise resemble other adult
species belonging to the same
group; for the latter are the
living proofs that such a state
of things was formerly possible.
Young lions and pumas are marked
with feeble stripes or rows of
spots, and as many allied species
both young and old are similarly
marked, no believer in evolution
will doubt that the progenitor
of the lion and puma was a striped
animal, and that the young have
retained vestiges of the stripes,
like the kittens of black cats,
which are not in the least striped
when grown up. Many species of
deer, which when mature are not
spotted, are whilst young covered
with white spots, as are likewise
some few species in the adult
state. So again the young in
the whole family of pigs (Suidae),
and in certain rather distantly
allied animals, such as the tapir,
are marked with dark longitudinal
stripes; but here we have a character
apparently derived from an extinct
progenitor, and now preserved
by the young alone. In all such
cases the old have had their
colours changed in the course
of time, whilst the young have
remained but little altered,
and this has been effected through
the principle of inheritance
at corresponding ages.
This same principle applies
to many birds belonging to various
groups, in which the young closely
resemble each other, and differ
much from their respective adult
parents. The young of almost
all the Gallinaceae, and of some
distantly allied birds such as
ostriches, are covered with longitudinally
striped down; but this character
points back to a state of things
so remote that it hardly concerns
us. Young cross-bills (Loxia)
have at first straight beaks
like those of other finches,
and in their immature striated
plumage they resemble the mature
red-pole and female siskin, as
well as the young of the goldfinch,
greenfinch, and some other allied
species. The young of many kinds
of buntings (Emberiza) resemble
one another, and likewise the
adult state of the common bunting,
E. miliaria. In almost the whole
large group of thrushes the young
have their breasts spotted- a
character which is retained throughout
life by many species, but is
quite lost by others, as by the
Turdus migratorius. So again
with many thrushes, the feathers
on the back are mottled before
they are moulted for the first
time, and this character is retained
for life by certain eastern species.
The young of many species of
shrikes (Lanius), of some woodpeckers,
and of an Indian pigeon (Chalcophaps
indicus), are transversely striped
on the under surface; and certain
allied species or whole genera
are similarly marked when adult.
In some closely-allied and resplendent
Indian cuckoos (Chrysococcyx),
the mature species differ considerably
from one another in colour, but
the young cannot be distinguished.
The young of an Indian goose
(Sarkidiornis melanonotus) closely
resemble in plumage an allied
genus, Dendrocygna, when mature.*
Similar facts will hereafter
be given in regard to certain
herons. Young black-grouse (Tetrao
tetrix) resemble the young as
well as the old of certain other
species, for instance the red-grouse
or T. scoticus. Finally, as Mr.
Blyth, who has attended closely
to this subject, has well remarked,
the natural affinities of many
species are best exhibited in
their immature plumage; and as
the true affinities of all organic
beings depend on their descent
from a common progenitor, this
remark strongly confirms the
belief that the immature plumage
approximately shews us the former
or ancestral condition of the
species.
* In regard to thrushes, shrikes,
and woodpeckers, see Mr. Blyth,
in Charlesworth's Mag. of Nat.
Hist., vol. i., 1837, p. 304;
also footnote to his translation
of Cuvier's Regne Animal, p.
159. I give the case of Loxia
on Mr. Blyth's information. On
thrushes, see also Audubon, Ornith.
Biog., vol. ii., p. 195. On Chrysococcyx
and Chalcophaps, Blyth, as quoted
in Jerdon's Birds of India, vol.
iii., p. 485. On Sarkidiornis,
Blyth, in Ibis, 1867, p. 175.
Although many young birds, belonging
to various families, thus give
us a glimpse of the plumage of
their remote progenitors, yet
there are many other birds, both
dull-coloured and bright-coloured,
in which the young closely resemble
their parents. In such cases
the young of the different species
cannot resemble each other more
closely than do the parents;
nor can they strikingly resemble
allied forms when adult. They
give us but little insight into
the plumage of their progenitors,
excepting in so far that, when
the young and the old are coloured
in the same general manner throughout
a whole group of species, it
is probable that their progenitors
were similarly coloured.
We may now consider the classes
of cases, under which the differences
and resemblances between the
plumage of the young and the
old, in both sexes or in one
sex alone, may be grouped. Rules
of this kind were first enounced
by Cuvier; but with the progress
of knowledge they require some
modification and amplification.
This I have attempted to do,
as far as the extreme complexity
of the subject permits, from
information derived from various
sources; but a full essay on
this subject by some competent
ornithologist is much needed.
In order to ascertain to what
extent each rule prevails, I
have tabulated the facts given
in four great works, namely,
by Macgillivray on the birds
of Britain, Audubon on those
of North America, Jerdon on those
of India, and Gould on those
of Australia. I may here premise,
first, that the several cases
or rules graduate into each other;
and secondly, that when the young
are said to resemble their parents,
it is not meant that they are
identically alike, for their
colours are almost always less
vivid, and the feathers are softer
and often of a different shape.
RULES OR CLASSES OF CASES.
I When the adult male is more
beautiful or conspicuous than
the adult female, the young of
both sexes in their first plumage
closely resemble the adult female,
as with the common fowl and peacock;
or, as occasionally occurs. they
resemble her much more closely
than they do the adult male.
II When the adult female is
more conspicuous than the adult
male, as sometimes though rarely
occurs, the young of both sexes
in their first plumage resemble
the adult male.
III When the adult male resembles
the adult female, the young of
both sexes have a peculiar first
plumage of their own, as with
the robin.
IV When the adult male resembles
the adult female, the young of
both sexes in their first plumage
resemble the adults, as with
the kingfisher, many parrots,
crows, hedge-warblers.
V When the adults of both sexes
have a distinct winter and summer
plumage, whether or not the male
differs from the female, the
young resemble the adults of
both sexes in their winter dress,
or much more rarely in their
summer dress, or they resemble
the females alone. Or the young
may have an intermediate character;
or again they may differ greatly
from the adults in both their
seasonal plumages.
VI In some few cases the young
in their first plumage differ
from each other according to
sex; the young males resembling
more or less closely the adult
males, and the young females
more or less closely the adult
females.
CLASS I In this class, the young
of both sexes more or less closely
resemble the adult female, whilst
the adult male differs from the
adult female, often in the most
conspicuous manner. Innumerable
instances in all Orders could
be given; it will suffice to
call to mind the common pheasant,
duck, and house-sparrow. The
cases under this class graduate
into others. Thus the two sexes
when adult may differ so slightly,
and the young so slightly from
the adults, that it is doubtful
whether such cases ought to come
under the present, or under the
third or fourth classes. So again
the young of the two sexes, instead
of being quite alike, may differ
in a slight degree from each
other, as in our sixth class.
These transitional cases, however,
are few, or at least are not
strongly pronounced, in comparison
with those which come strictly
under the present class.
The force of
the present law is well shewn
in those groups,
in which, as a general rule,
the two sexes and the young are
all alike; for when in these
groups the male does differ from
the female, as with certain parrots,
kingfishers, pigeons, &c., the
young of both sexes resemble
the adult female.* We see the
same fact exhibited still more
clearly in certain anomalous
cases; thus the male of Heliothrix
auriculata (one of the humming-birds)
differs conspicuously from the
female in having a splendid gorget
and fine ear-tufts, but the female
is remarkable from having a much
longer tail than that of the
male; now the young of both sexes
resemble (with the exception
of the breast being spotted with
bronze) the adult female in all
other respects, including the
length of her tail, so that the
tail of the male actually becomes
shorter as he reaches maturity,
which is a most unusual circumstance.*(2)
Again, the plumage of the male
goosander (Mergus merganser)
is more conspicuously coloured
than that of the female, with
the scapular and secondary wing-feather
much longer; but differently
from what occurs, as far as I
know, in any other bird, the
crest of the adult male, though
broader than that of the female,
is considerably shorter, being
only a little above an inch in
length; the crest of the female
being two and a half inches long.
Now the young of both sexes entirely
resemble the adult female, so
that their crests are actually
of greater length, though narrower,
than in the adult male.*(3)
* See, for instance, Mr. Gould's
account (Handbook of the Birds
of Australia, vol. i., p. 133)
of Cyanalcyon (one of the Kingfishers),
in which, however, the young
male, though resembling the adult
female, is less brilliantly coloured.
In some species of Dacelo the
males have blue tails, and the
females brown ones; and Mr. R.
B. Sharpe informs me that the
tail of the young male of D.
gaudichaudi is at first brown.
Mr. Gould has described (ibid.,
vol. ii., pp. 14, 20, 37) the
sexes and the young of certain
black cockatoos and of the king
lory, with which the same rule
prevails. Also Jerdon (Birds
of India, vol. i., p. 260) on
the Paloeornis rosa, in which
the young are more like the female
than the male. See Audubon (Ornithological
Biography, vol. ii., p. 475)
on the two sexes and the young
of Columba passerina.
*(2) I owe this information
to Mr. Gould, who shewed me the
specimens; see also his Introduction
to the Trochilidae, 1861, p.
120.
*(3) Macgillivray, Hist. Brit.
Birds, vol. v., pp. 207-214.
When the young and the females
closely resemble each other and
both differ from the males, the
most obvious conclusion is that
the males alone have been modified.
Even in the anomalous cases of
the Heliothrix and Mergus, it
is probable that originally both
adult sexes were furnished- the
one species with a much elongated
tail, and the other with a much
elongated crest- these characters
having since been partially lost
by the adult males from some
unexplained cause, and transmitted
in their diminished state to
their male offspring alone, when
arrived at the corresponding
age of maturity. The belief that
in the present class the male
alone has been modified, as far
as the differences between the
male and the female together
with her young are concerned,
is strongly supported by some
remarkable facts recorded by
Mr. Blyth,* with respect to closely-allied
species which represent each
other in distinct countries.
For with several of these representative
species the adult males have
undergone a certain amount of
change and can be distinguished;
the females and the young from
the distinct countries being
indistinguishable, and therefore
absolutely unchanged. This is
the case with certain Indian
chats (Thamnobia), with certain
honey-suckers (Nectarinia), shrikes
(Tephrodornis), certain kingfishers
(Tanysiptera), Kalij pheasants
(Gallophasis), and tree-partridges
(Arboricola).
* See his admirable paper in
the Journal of the Asiatic Soc.
of Bengal, vol. xix., 1850, p.
223; see also Jerdon, Birds of
India, vol. i., introduction,
p. xxix. In regard to Tanysiptera,
Prof. Schlegel told Mr. Blyth
that he could distinguish several
distinct races, solely by comparing
the adult males.
In some analogous
cases, namely with birds having
a different
summer and winter plumage, but
with the two sexes nearly alike,
certain closely-allied species
can easily be distinguished in
their summer or nuptial plumage,
yet are indistinguishable in
their winter as well as in their
immature plumage. This is the
case with some of the closely-allied
Indian wagtails or Motacillae.
Mr. Swinhoe* informs me that
three species of Ardeola, a genus
of herons, which represent one
another on separate continents,
are "most strikingly different" when
ornamented with their summer
plumes, but are hardly, if at
all, distinguishable during the
winter. The young also of these
three species in their immature
plumage closely resemble the
adults in their winter dress.
This case is all the more interesting,
because with two other species
of Ardeola both sexes retain,
during the winter and summer,
nearly the same plumage as that
possessed by the three first
species during the winter and
in their immature state; and
this plumage, which is common
to several distinct species at
different ages and seasons, probably
shews us how the progenitors
of the genus were coloured. In
all these cases, the nuptial
plumage which we may assume was
originally acquired by the adult
males during the breeding-season,
and transmitted to the adults
of both sexes at the corresponding
season, has been modified, whilst
the winter and immature plumages
have been left unchanged.
* See also Mr. Swinhoe, in Ibis,
July, 1863, p. 131; and a previous
paper, with an extract from a
note by Mr. Blyth, in Ibis, January,
1861, p. 25.
The question naturally arises,
how is it that in these latter
cases the winter plumage of both
sexes, and in the former cases
the plumage of the adult females,
as well as the immature plumage
of the young, have not been at
all affected? The species which
represent each other in distinct
countries will almost always
have been exposed to somewhat
different conditions, but we
can hardly attribute to this
action the modification of the
plumage in the males alone, seeing
that the females and the young,
though similarly exposed, have
not been affected. Hardly any
fact shews us more clearly how
subordinate in importance is
the direct action of the conditions
of life, in comparison with the
accumulation through selection
of indefinite variations, than
the surprising difference between
the sexes of many birds; for
both will have consumed the same
food, and have been exposed to
the same climate. Nevertheless
we are not precluded from believing
that in the course of time new
conditions may produce some direct
effect either on both sexes,
or from their constitutional
differences chiefly on one sex.
We see only that this is subordinate
in importance to the accumulated
results of selection. Judging,
however, from a wide-spread analogy,
when a species migrates into
a new country (and this must
precede the formation of representative
species), the changed conditions
to which they will almost always
have been exposed will cause
them to undergo a certain amount
of fluctuating variability. In
this case sexual selection, which
depends on an element liable
to change- the taste or admiration
of the female- will have had
new shades of colour or other
differences to act on and accumulate;
and as sexual selection is always
at work, it would (from what
we know of the results on domestic
animals of man's unintentional
selection), be surprising if
animals inhabiting separate districts,
which can never cross and thus
blend their newly-acquired characters,
were not, after a sufficient
lapse of time, differently modified.
These remarks likewise apply
to the nuptial or summer plumage,
whether confined to the males,
or common to both sexes.
Although the
females of the above closely-allied
or representative
species, together with their
young, differ hardly at all from
one another, so that the males
alone can be distinguished, yet
the females of most species within
the same genus obviously differ
from each other. The differences,
however, are rarely as great
as between the males. We see
this clearly in the whole family
of the Gallinaceae: the females,
for instance, of the common and
Japan pheasant, and especially
of the gold and Amherst pheasant-
of the silver pheasant and the
wild fowl- resemble one another
very closely in colour, whilst
the males differ to an extraordinary
degree. So it is with the females
of most of the Cotingidae, Fringillidae,
and many other families. There
can indeed be no doubt that,
as a general rule, the females
have been less modified than
the males. Some few birds, however,
offer a singular and inexplicable
exception; thus the females of
Paradisea apoda and P. papuana
differ from each other more than
do their respective males;* the
female of the latter species
having the under surface pure
white, whilst the female P. apoda
is deep brown beneath. So, again,
as I hear from Professor Newton,
the males of two species of Oxynotus
(shrikes), which represent each
other in the islands of Mauritius
and Bourbon,*(2) differ but little
in colour, whilst the females
differ much. In the Bourbon species
the female appears to have partially
retained an immature condition
of plumage, for at first sight
she "might be taken for the young
of the Mauritian species." These
differences may be compared with
those inexplicable ones, which
occur independently of man's
selection in certain sub-breeds
of the game-fowl, in which the
females are very different, whilst
the males can hardly be distinguished.*(3)
* Wallace, The Malay Archipelago,
vol. ii., 1869, p. 394.
*(2) These species are described
with coloured figures, by M.
F. Pollen, in Ibis, 1866, p.
275.
*(3) Variation
of Animals, &c.,
vol. i., p. 251.
As I account
so largely by sexual selection
for the differences
between the males of allied species,
how can the differences between
the females be accounted for
in all ordinary cases? We need
not here consider the species
which belong to distinct genera;
for with these, adaptation to
different habits of life, and
other agencies, will have come
into play. In regard to the differences
between the females within the
same genus, it appears to me
almost certain, after looking
through various large groups,
that the chief agent has been
the greater or less transference
to the female of the characters
acquired by the males through
sexual selection. In the several
British finches, the two sexes
differ either very slightly or
considerably; and if we compare
the females of the greenfinch,
chaffinch, goldfinch, bullfinch,
crossbill, sparrow, &c., we shall
see that they differ from one
another chiefly in the points
in which they partially resemble
their respective males; and the
colours of the males may safely
be attributed to sexual selection.
With many gallinaceous species
the sexes differ to an extreme
degree, as with the peacock,
pheasant, and fowl, whilst with
other species there has been
a partial or even complete transference
of character from the male to
the female. The females of the
several species of Polyplectron
exhibit in a dim condition, and
chiefly on the tail, the splendid
ocelli of their males. The female
partridge differs from the male
only in the red mark on her breast
being smaller; and the female
wild turkey only in her colours
being much duller. In the guinea-fowl
the two sexes are indistinguishable.
There is no improbability in
the plain, though peculiarly
spotted plumage of this latter
bird having been acquired through
sexual selection by the males,
and then transmitted to both
sexes; for it is not essentially
different from the much more
beautifully spotted plumage,
characteristic of the males alone
of the tragopan pheasants.
It should be observed that,
in some instances, the transference
of characters from the male to
the female has been effected
apparently at a remote period,
the male having subsequently
undergone great changes, without
transferring to the female any
of his later-gained characters.
For instance, the female and
the young of the black-grouse
(Tetrao tetrix) resemble pretty
closely both sexes and the young
of the red-grouse (T. scoticus);
and we may consequently infer
that the black-grouse is descended
from some ancient species, of
which both sexes were coloured
in nearly the same manner as
the red-grouse. As both sexes
of this latter species are more
distinctly barred during the
breeding-season than at any other
time, and as the male differs
slightly from the female in his
more strongly-pronounced red
and brown tints,* we may conclude
that his plumage has been influenced
by sexual selection, at least
to a certain extent. If so, we
may further infer that nearly
similar plumage of the female
black-grouse was similarly produced
at some former period. But since
this period the male black-grouse
has acquired his fine black plumage,
with his forked and outwardly-curled
tail-feathers; but of these characters
there has hardly been any transference
to the female, excepting that
she shews in her tail a trace
of the curved fork.
* Macgillivray, History of British
Birds, vol. i., pp. 172-174.
We may therefore
conclude that the females of
distinct though
allied species have often had
their plumage rendered more or
less different by the transference
in various degrees of characters
acquired by the males through
sexual selection, both during
former and recent times. But
it deserves especial attention
that brilliant colours have been
transferred much more rarely
than other tints. For instance,
the male of the red-throated
blue-breast (Cyanecula suecica)
has a rich blue breast, including
a sub-triangular red mark; now
marks of nearly the same shape
have been transferred to the
female, but the central space
is fulvous instead of red, and
is surrounded by mottled instead
of blue feathers. The Gallinaceae
offer many analogous cases; for
none of the species, such as
partridges, quails, guinea-fowls, &c.,
in which the colours of the plumage
have been largely transferred
from the male to the female,
are brilliantly coloured. This
is well exemplified with the
pheasants, in which the male
is generally so much more brilliant
than the female; but with the
Eared and Cheer pheasants (Crossoptilon
auritum and Phasianus wallichii)
the sexes closely resemble each
other and their colours are dull.
We may go so far as to believe
that if any part of the plumage
in the males of these two pheasants
had been brilliantly coloured,
it would not have been transferred
to the females. These facts strongly
support Mr. Wallace's view that
with birds which are exposed
to much danger during incubation,
the transference of bright colours
from the male to the female has
been checked through natural
selection. We must not, however,
forget that another explanation,
before given, is possible; namely,
that the males which varied and
became bright, whilst they were
young and inexperienced, would
have been exposed to much danger,
and would generally have been
destroyed; the older and more
cautious males, on the other
hand, if they varied in a like
manner, would not only have been
able to survive, but would have
been favoured in their rivalry
with other males. Now variations
occurring late in life tend to
be transmitted exclusively to
the same sex, so that in this
case extremely bright tints would
not have been transmitted to
the females. On the other hand,
ornaments of a less conspicuous
kind, such as those possessed
by the Eared and Cheer pheasants,
would not have been dangerous,
and if they appeared during early
youth, would generally have been
transmitted to both sexes.
In addition to the effects of
the partial transference of characters
from the males to the females,
some of the differences between
the females of closely-allied
species may be attributed to
the direct or definite action
of the conditions of life.* With
the males, any such action would
generally have been masked by
the brilliant colours gained
through sexual selection; but
not so with the females. Each
of the endless diversities in
plumage which we see in our domesticated
birds is, of course, the result
of some definite cause; and under
natural and more uniform conditions,
some one tint, assuming that
it was in no way injurious, would
almost certainly sooner or later
prevail. The free intercrossing
of the many individuals belonging
to the same species would ultimately
tend to make any change of colour,
thus induced, uniform in character.
* See, on this subject, chap.
xxiii. in the Variation of Animals
and Plants under Domestication.
No one doubts that both sexes
of many birds have had their
colours adapted for the sake
of protection; and it is possible
that the females alone of some
species may have been modified
for this end. Although it would
be a difficult, perhaps an impossible
process, as shewn in the last
chapter, to convert one form
of transmission into another
through selection, there would
not be the least difficulty in
adapting the colours of the female,
independently of those of the
male, to surrounding objects,
through the accumulation of variations
which were from the first limited
in their transmission to the
female sex. If the variations
were not thus limited, the bright
tints of the male would be deteriorated
or destroyed. Whether the females
alone of many species have been
thus specially modified, is at
present very doubtful. I wish
I could follow Mr. Wallace to
the full extent; for the admission
would remove some difficulties.
Any variations which were of
no service to the female as a
protection would be at once obliterated,
instead of being lost simply
by not being selected, or from
free intercrossing, or from being
eliminated when transferred to
the male and in any way injurious
to him. Thus the plumage of the
female would be kept constant
in character. It would also be
a relief if we could admit that
the obscure tints of both sexes
of many birds had been acquired
and preserved for the sake of
protection,- for example, of
the hedge-warbler or kitty-wren
(Accentor modularis and Troglodytes
vulgaris), with respect to which
we have no sufficient evidence
of the action of sexual selection.
We ought, however, to be cautious
in concluding that colours which
appear to us dull, are not attractive
to the females of certain species;
we should bear in mind such cases
as that of the common house-sparrow,
in which the male differs much
from the female, but does not
exhibit any bright tints. No
one probably will dispute that
many gallinaceous birds which
live on the open ground, have
acquired their present colours,
at least in part, for the sake
of protection. We know how well
they are thus concealed; we know
that ptarmigans, whilst changing
from their winter to their summer
plumage, both of which are protective,
suffer greatly from birds of
prey. But can we believe that
the very slight differences in
tints and markings between, for
instance, the female black-grouse
and red-grouse serve as a protection?
Are partridges, as they are now
coloured, better protected than
if they had resembled quails?
Do the slight differences between
the females of the common pheasant,
the Japan and gold pheasants,
serve as a protection, or might
not their plumages have been
interchanged with impunity? From
what Mr. Wallace has observed
of the habits of certain gallinaceous
birds in the East, he thinks
that such slight differences
are beneficial. For myself, I
will only say that I am not convinced.
Formerly when
I was inclined to lay much
stress on protection
as accounting for the duller
colours of female birds, it occurred
to me that possibly both sexes
and the young might aboriginally
have been equally bright coloured;
but that subsequently, the females
from the danger incurred during
incubation, and the young from
being inexperienced, had been
rendered dull as a protection.
But this view is not supported
by any evidence, and is not probable;
for we thus in imagination expose
during past times the females
and the young to danger, from
which it has subsequently been
necessary to shield their modified
descendants. We have, also, to
reduce, through a gradual process
of selection, the females and
the young to almost exactly the
same tints and markings, and
to transmit them to the corresponding
sex and period of life. On the
supposition that the females
and the young have partaken during
each stage of the process of
modification of a tendency to
be as brightly coloured as the
males, it is also a somewhat
strange fact that the females
have never been rendered dull-coloured
without the young participating
in the same change; for there
are no instances, as far as I
can discover, of species with
the females dull and the young
bright coloured. A partial exception,
however, is offered by the young
of certain woodpeckers, for they
have "the whole upper part of
the head tinged with red," which
afterwards either decreases into
a mere circular red line in the
adults of both sexes, or quite
disappears in the adult females.*
* Audubon, Ornith. Biography,
vol. i., p. 193. Macgillivray,
History of British Birds, vol.
iii., p. 85. See also the case
before given of Indopicus carlotta.
Finally, with respect to our
present class of cases, the most
probable view appears to be that
successive variations in brightness
or in other ornamental characters,
occurring in the males at a rather
late period of life have alone
been preserved; and that most
or all of these variations, owing
to the late period of life at
which they appeared, have been
from the first transmitted only
to the adult male offspring.
Any variations in brightness
occurring in the females or in
the young, would have been of
no service to them, and would
not have been selected; and moreover,
if dangerous, would have been
eliminated. Thus the females
and the young will either have
been left unmodified, or (as
is much more common) will have
been partially modified by receiving
through transference from the
males some of his successive
variations. Both sexes have perhaps
been directly acted on by the
conditions of life to which they
have long been exposed: but the
females from not being otherwise
much modified, will best exhibit
any such effects. These changes
and all others will have been
kept uniform by the free intercrossing
of many individuals. In some
cases, especially with ground
birds, the females and the young
may possibly have been modified,
independently of the males, for
the sake of protection, so as
to have acquired the same dull-coloured
plumage.
CLASS II When the adult female
is more conspicuous than the
adult male, the young of both
sexes in their first plumage
resemble the adult male.- This
class is exactly the reverse
of the last, for the females
are here brighter coloured or
more conspicuous than the males;
and the young, as far as they
are known, resemble the adult
males instead of the adult females.
But the difference between the
sexes is never nearly so great
as with many birds in the first
class, and the cases are comparatively
rare. Mr. Wallace, who first
called attention to the singular
relation which exists between
the less bright colours of the
males and their performing the
duties of incubation, lays great
stress on this point,* as a crucial
test that obscure colours have
been acquired for the sake of
protection during the period
of nesting. A different view
seems to me more probable. As
the cases are curious and not
numerous, I will briefly give
all that I have been able to
find.
* Westminster Review, July,
1867, and A. Murray, Journal
of Travel, 1868, p. 83.
In one section
of the genus Turnix, quail-like
birds, the
female is invariably larger than
the male (being nearly twice
as large in one of the Australian
species), and this is an unusual
circumstance with the Gallinaceae.
In most of the species the female
is more distinctly coloured and
brighter than the male,* but
in some few species the sexes
are alike. In Turnix taigoor
of India the male "wants the
black on the throat and neck,
and the whole tone of the plumage
is lighter and less pronounced
than that of the female." The
female appears to be noisier,
and is certainly much more pugnacious
than the male; so that the females
and not the males are often kept
by the natives for fighting,
like game-cocks. As male birds
are exposed by the English bird-catchers
for a decoy near a trap, in order
to catch other males by exciting
their rivalry, so the females
of this Turnix are employed in
India. When thus exposed the
females soon begin their "loud
purring call, which can be heard
a long way off, and any females
within ear-shot run rapidly to
the spot, and commence fighting
with the bird." In this way from
twelve to twenty birds, all breeding
females, may be caught in the
course of a single day. The natives
assert that the females after
laying their eggs associate in
flocks, and leave the males to
sit on them. There is no reason
to doubt the truth of this assertion,
which is supported by some observations
made in China by Mr. Swinhoe.*(2)
Mr. Blyth believes, that the
young of both sexes resemble
the adult male.
* For the Australian
species, see Gould's Handbook, &c.,
vol. ii., pp. 178, 180, 186,
and 188.
In the British Museum specimens
of the Australian plain-wanderer
(Pedionomus torquatus) may be
seen, shewing similar sexual
differences.
*(2) Jerdon, Birds of India,
vol. iii., p. 596. Mr. Swinhoe,
in Ibis, 1865, p. 542; 1866,
pp. 131, 405.
The females
of the three species of painted
snipes (see Rhynchoea,
fig. 62) "are not only larger
but much more richly coloured
than the males."* With all other
birds in which the trachea differs
in structure in the two sexes
it is more developed and complex
in the male than in the female;
but in the Rhynchoea australis
it is simple in the male, whilst
in the female it makes four distinct
convolutions before entering
the lungs.*(2) The female therefore
of this species has acquired
an eminently masculine character.
Mr. Blyth ascertained, by examining
many specimens, that the trachea
is not convoluted in either sex
of R. bengalensis, which species
resembles R. australis so closely,
that it can hardly be distinguished
except by its shorter toes. This
fact is another striking instance
of the law that secondary sexual
characters are often widely different
in closely-allied forms, though
it is a very rare circumstance
when such differences relate
to the female sex. The young
of both sexes of R. bengalensis
in their first plumage are said
to resemble the mature male.*(3)
There is also reason to believe
that the male undertakes the
duty of incubation, for Mr. Swinhoe*(4)
found the females before the
close of the summer associated
in flocks, as occurs with the
females of the Turnix.
* Jerdon, Birds of India, vol.
iii., p. 677.
*(2) Gould's Handbook of the
Birds of Australia, vol. ii.,
p. 275.
*(3) The Indian Field, Sept.,
1858, p. 3.
*(4) Ibis, 1866, p. 298.
The females
of Phalaropus fulicarius and
P. hyperboreus are larger,
and in their summer plumage "more
gaily attired than the males." But
the difference in colour between
the sexes is far from conspicuous.
According to Professor Steenstrup,
the male alone of P. fulicarius
undertakes the duty of incubation;
this is likewise shewn by the
state of his breast-feathers
during the breeding-season. The
female of the dotterel plover
(Eudromias morinellus) is larger
than the male, and has the red
and black tints on the lower
surface, the white crescent on
the breast, and the stripes over
the eyes, more strongly pronounced.
The male also takes at least
a share in hatching the eggs;
but the female likewise attends
to the young.* I have not been
able to discover whether with
these species the young resemble
the adult males more closely
than the adult females; for the
comparison is somewhat difficult
to make on account of the double
moult.
* For these
several statements, see Mr.
Gould's Birds of Great
Britain. Prof. Newton informs
me that he has long been convinced,
from his own observations and
from those of others, that the
males of the above-named species
take either the whole or a large
share of the duties of incubation,
and that they "shew much greater
devotion towards their young,
when in danger, than do the females." So
it is, as he informs me, with
Limosa lapponica and some few
other waders, in which the females
are larger and have more strongly
contrasted colours than the males.
Turning now
to the ostrich Order: the male
of the common cassowary
(Casuarius galeatus) would be
thought by any one to be the
female, from his smaller size
and from the appendages and naked
skin about his head being much
less brightly coloured; and I
am informed by Mr. Bartlett that
in the Zoological Gardens, it
is certainly the male alone who
sits on the eggs and takes care
of the young.* The female is
said by Mr. T. W. Wood*(2) to
exhibit during the breeding-season
a most pugnacious disposition;
and her wattles then become enlarged
and more brilliantly coloured.
So again the female of one of
the emus (Dromoeus irroratus)
is considerably larger than the
male, and she possesses a slight
top-knot, but is otherwise indistinguishable
in plumage. She appears, however, "to
have greater power, when angry
or otherwise excited, of erecting,
like a turkey-cock, the feathers
of her neck and breast. She is
usually the more courageous and
pugilistic. She makes a deep
hollow guttural boom especially
at night, sounding like a small
gong. The male has a slenderer
frame and is more docile, with
no voice beyond a suppressed
hiss when angry, or a croak." He
not only performs the whole duty
of incubation, but has to defend
the young from their mother; "for
as soon as she catches sight
of her progeny she becomes violently
agitated, and notwithstanding
the resistance of the father
appears to use her utmost endeavours
to destroy them. For months afterwards
it is unsafe to put the parents
together, violent quarrels being
the inevitable result, in which
the female generally comes off
conqueror."*(3) So that with
this emu we have a complete reversal
not only of the parental and
incubating instincts, but of
the usual moral qualities of
the two sexes; the females being
savage, quarrelsome, and noisy,
the males gentle and good. The
case is very different with the
African ostrich, for the male
is somewhat larger than the female
and has finer plumes with more
strongly contrasted colours;
nevertheless he undertakes the
whole duty of incubation.*(4)
* The natives of Ceram (Wallace,
Malay Archipelago, vol. ii.,
p. 150) assert that the male
and female sit alternately on
the eggs; but this assertion,
as Mr. Bartlett thinks, may be
accounted for by the female visiting
the nest to lay her eggs.
*(2) The Student, April, 1870,
p. 124.
*(3) See the excellent account
of the habits of this bird under
confinement, by Mr. A. W. Bennett,
in Land and Water, May, 1868,
p. 233.
*(4) Mr. Sclater, on the incubation
of the Struthiones, Proc. Zool.
Soc., June 9, 1863. So it is
with the Rhea darwinii: Captain
Musters says (At Home with the
Patagonians, 1871, p. 128), that
the male is larger, stronger
and swifter than the female,
and of slightly darker colours;
yet he takes sole charge of the
eggs and of the young, just as
does the male of the common species
of Rhea.
I will specify
the few other cases known to
me, in which the
female is more conspicuously
coloured than the male, although
nothing is known about the manner
of incubation. With the carrion-hawk
of the Falkland Islands (Milvago
leucurus) I was much surprised
to find by dissection that the
individuals, which had all their
tints strongly pronounced, with
the cere and legs orange-coloured,
were the adult females; whilst
those with duller plumage and
grey legs were the males or the
young. In an Australian tree-creeper
(Climacteris erythrops) the female
differs from the male in "being
adorned with beautiful, radiated,
rufous markings on the throat,
the male having this part quite
plain." Lastly, in an Australian
night-jar "the female always
exceeds the male in size and
in the brilliance of her tints;
the males, on the other hand,
have two white spots on the primaries
more conspicuous than in the
female."*
* For the Milvago, see Zoology
of the Voyage of the Beagle:
Birds, 1841, p. 16. For the Climacteris
and night-jar (Eurostopodus),
see Gould's Handbook of the Birds
of Australia, vol. i., pp. 602
and 97. The new Zealand shieldrake
(Tadorna variegata) offers a
quite anomalous case; the head
of the female is pure white,
and her back is redder than that
of the male; the head of the
male is of a rich dark bronzed
colour, and his back is clothed
with finely pencilled slate-coloured
feathers, so that altogether
he may be considered as the more
beautiful of the two. He is larger
and more pugnacious than the
female, and does not sit on the
eggs. So that in all these respects
this species comes under our
first class of cases; but Mr.
Sclater (Proceedings of the Zoological
Society, 1866, p. 150) was much
surprised to observe that the
young of both sexes, when about
three months old, resembled in
their dark heads and necks the
adult males, instead of the adult
females; so that it would appear
in this case that the females
have been modified, whilst the
males and the young have retained
a former state of plumage
We thus see that the cases in
which female birds are more conspicuously
coloured than the males, with
the young in their immature plumage
resembling the adult males instead
of the adult females, as in the
previous class, are not numerous,
though they are distributed in
various Orders. The amount of
difference, also, between the
sexes is incomparably less than
that which frequently occurs
in the last class; so that the
cause of the difference, whatever
it may have been, has here acted
on the females either less energetically
or less persistently than on
the males in the last class.
Mr. Wallace believes that the
males have had their colours
rendered less conspicuous for
the sake of protection during
the period of incubation; but
the difference between the sexes
in hardly any of the foregoing
cases appears sufficiently great
for this view to be safely accepted.
In some of the cases, the brighter
tints of the female are almost
confined to the lower surface,
and the males, if thus coloured,
would not have been exposed to
danger whilst sitting on the
eggs. It should also be borne
in mind that the males are not
only in a slight degree less
conspicuously coloured than the
females, but are smaller and
weaker. They have, moreover,
not only acquired the maternal
instinct of incubation, but are
less pugnacious and vociferous
than the females, and in one
instance have simpler vocal organs.
Thus an almost complete transposition
of the instincts, habits, disposition,
colour, size, and of some points
of structure, has been effected
between the two sexes.
Now if we might
assume that the males in the
present class
have lost some of that ardour
which is usual to their sex,
so that they no longer search
eagerly for the females; or,
if we might assume that the females
have become much more numerous
than the males- and in the case
of one Indian Turnix the females
are said to be "much more commonly
met with than the males"*- then
it is not improbable that the
females would have been led to
court the males, instead of being
courted by them. This indeed
is the case to a certain extent
with some birds, as we have seen
with the peahen, wild turkey,
and certain kinds of grouse.
Taking as our guide the habits
of most male birds, the greater
size and strength as well as
the extraordinary pugnacity of
the females of the Turnix and
emu, must mean that they endeavour
to drive away rival females,
in order to gain possession of
the male; and on this view all
the facts become clear; for the
males would probably be most
charmed or excited by the females
which were the most attractive
to them by their bright colours,
other ornaments, or vocal powers.
Sexual selection would then do
its work, steadily adding to
the attractions of the females;
the males and the young being
left not at all, or but little
modified.
* Jerdon, Birds of India, vol.
iii., p. 598.
CLASS Ill When the adult male
resembles the adult female, the
young of both sexes have a peculiar
first plumage of their own.-
In this class the sexes when
adult resemble each other, and
differ from the young. This occurs
with many birds of many kinds.
The male robin can hardly be
distinguished from the female,
but the young are widely different,
with their mottled dusky-olive
and brown plumage. The male and
female of the splendid scarlet
ibis are alike, whilst the young
are brown; and the scarlet colour,
though common to both sexes,
is apparently a sexual character,
for it is not well developed
in either sex under confinement;
and a loss of colour often occurs
with brilliant males when they
are confined. With many species
of herons the young differ greatly
from the adults; and the summer
plumage of the latter, though
common to both sexes, clearly
has a nuptial character. Young
swans are slate-coloured, whilst
the mature birds are pure white;
but it would be superfluous to
give additional instances. These
differences between the young
and the old apparently depend,
as in the last two classes, on
the young having retained a former
or ancient state of plumage,
whilst the old of both sexes
have acquired a new one. When
the adults are bright coloured,
we may conclude from the remarks
just made in relation to the
scarlet ibis and to many herons,
and from the analogy of the species
in the first class, that such
colours have been acquired through
sexual selection by the nearly
mature males; but that, differently
from what occurs in the first
two classes, the transmission,
though limited to the same age,
has not been limited to the same
sex. Consequently, the sexes
when mature resemble each other
and differ from the young.
CLASS IV When the adult male
resembles the adult female, the
young of both sexes in their
first plumage resemble the adults.-
In this class the young and the
adults of both sexes, whether
brilliantly or obscurely coloured,
resemble each other. Such cases
are, I think, more common than
those in the last class. We have
in England instances in the kingfisher,
some woodpeckers, the jay, magpie,
crow, and many small dull-coloured
birds, such as the hedge-warbler
or kitty-wren. But the similarity
in plumage between the young
and the old is never complete,
and graduates away into dissimilarity.
Thus the young of some members
of the kingfisher family are
not only less vividly coloured
than the adults, but many of
the feathers on the lower surface
are edged with brown,*- a vestige
probably of a former state of
the plumage. Frequently in the
same group of birds, even within
the same genus, for instance
in an Australian genus of parrakeets
(Platycercus), the young of some
species closely resemble, whilst
the young of other species differ
considerably from, their parents
of both sexes, which are alike.*(2)
Both sexes and the young of the
common jay are closely similar;
but in the Canada jay (Perisoreus
canadensis) the young differ
so much from their parents that
they were formerly described
as distinct species.*(3)
* Jerdon, Birds of India, vol.
i., pp. 222, 228. Gould's Handbook
to the Birds of Australia, vol.
i., pp. 124, 130.
*(2) Gould, ibid., vol. ii.,
pp. 37, 46, 56.
*(3) Audubon, Ornith. Biography,
vol. ii., p. 55.
I may remark before proceeding
that, under the present and next
two classes of cases, the facts
are so complex and the conclusions
so doubtful, that any one who
feels no especial interest in
the subject had better pass them
over.
The brilliant or conspicuous
colours which characterise many
birds in the present class, can
rarely or never be of service
to them as a protection; so that
they have probably been gained
by the males through sexual selection,
and then transferred to the females
and the young. It is, however,
possible that the males may have
selected the more attractive
females; and if these transmitted
their characters to their offspring
of both sexes, the same results
would follow as from the selection
of the more attractive males
by the females. But there is
evidence that this contingency
has rarely, if ever, occurred
in any of those groups of birds
in which the sexes are generally
alike; for, if even a few of
the successive variations had
failed to be transmitted to both
sexes, the females would have
slightly exceeded the males in
beauty. Exactly the reverse occurs
under nature; for, in almost
every group in which the sexes
generally resemble each other,
the males of some few species
are in a slight degree more brightly
coloured than the females. It
is again possible that the females
may have selected the more beautiful
males, these males having reciprocally
selected the more beautiful females;
but it is doubtful whether this
double process of selection would
be likely to occur, owing to
the greater eagerness of one
sex than the other, and whether
it would be more efficient than
selection on one side alone.
It is, therefore, the most probable
view that sexual selection has
acted, in the present class,
as far as ornamental characters
are concerned, in accordance
with the general rule throughout
the animal kingdom, that is,
on the males; and that these
have transmitted their gradually-acquired
colours, either equally or almost
equally, to their offspring of
both sexes.
Another point is more doubtful,
namely, whether the successive
variations first appeared in
the males after had become nearly
mature, or whilst quite young.
In either case sexual selection
must have acted on the male when
he had to compete with rivals
for the possession of the female;
and in both cases the characters
thus acquired have been transmitted
to both sexes and all ages. But
these characters if acquired
by the males when adult, may
have been transmitted at first
to the adults alone, and at some
subsequent period transferred
to the young. For it is known
that, when the law of inheritance
at corresponding ages fails,
the offspring often inherit characters
at an earlier age than that at
which they first appeared in
their parents.* Cases apparently
of this kind have been observed
with birds in a state of nature.
For instance Mr. Blyth has seen
specimens of Lanius rufus and
of Colymbus glacialis which had
assumed whilst young, in a quite
anomalous manner, the adult plumage
of their parents.*(2) Again,
the young of the common swan
(Cygnus olor) do not cast off
their dark feathers and become
white until eighteen months or
two years old; but Dr. F. Forel
has described the case of three
vigorous young birds, out of
a brood of four, which were born
pure white. These young birds
were not albinos, as shewn by
the color of their beaks and
legs, which nearly resembled
the same parts in the adults.*(3)
* Variation of Animals and Plants
under Domestication, vol. ii.,
p. 79.
*(2) Charlesworth's Magazine
of Natural History, vol. i.,
1837, pp. 305, 306.
*(3) Bulletin de la Soc. Vaudoise
des Sc. Nat., vol. x., 1869,
p. 132. The young of the Polish
swan, Cygnus immutabilis of Yarrell,
are always white; but this species,
as Mr. Sclater informs me, is
believed to be nothing more than
a variety of the domestic swan
(Cygnus olor).
It may be worth while to illustrate
the above three modes by which,
in the present class, the two
sexes and the young may have
come to resemble each other,
by the curious case of the genus
Passer.* In the house-sparrow
(P. domesticus) the male differs
much from the female and from
the young. The young and the
females are alike, and resemble
to a large extent both sexes
and the young of the sparrow
of Palestine (P. brachydactylus),
as well as of some allied species.
We may therefore assume that
the female and young of the house-sparrow
approximately shew us the plumage
of the progenitor of the genus.
Now with the tree-sparrow (P.
montanus) both sexes and the
young closely resemble the male
of the house-sparrow; so that
they have all been modified in
the same manner, and all depart
from the typical colouring of
their early progenitor. This
may have been effected by a male
ancestor of the tree-sparrow
having varied, firstly, when
nearly mature; or, secondly,
whilst quite young, and by having
in either case transmitted his
modified plumage to the females
and the young; or, thirdly, he
may have varied when adult and
transmitted his plumage to both
adult sexes, and, owing to the
failure of the law of inheritance
at corresponding ages, at some
subsequent period to his young.
* I am indebted to Mr. Blyth
for information in regard to
this genus. The sparrow of Palestine
belongs to the sub-genus Petronia.
It is impossible to decide which
of these three modes has generally
prevailed throughout the present
class of cases. That the males
varied whilst young, and transmitted
their variations to their offspring
of both sexes, is the most probable.
I may here add that I have, with
little success, endeavoured,
by consulting various works,
to decide how far the period
of variation in birds has generally
determined the transmission of
characters to one sex or to both.
The two rules, often referred
to (namely, that variations occurring
late in life are transmitted
to one and the same sex, whilst
those which occur early in life
are transmitted to both sexes),
apparently hold good in the first,*
second, and fourth classes of
cases; but they fail in the third,
often in the fifth,*(2) and in
the sixth small class. They apply,
however, as far as I can judge,
to a considerable majority of
the species; and we must not
forget the striking generalisation
by Dr. W. Marshall with respect
to the protuberances on the heads
of birds. Whether or not the
two rules generally hold good,
we may conclude from the facts
given in the eighth chapter,
that the period of variation
is one important element in determining
the form of transmission.
* For instance, the males of
Tanagra aestiva and Fringilla
cyanea require three years, the
male of Fringilla ciris four
years, to complete their beautiful
plumage. (See Audubon, Ornith.
Biography, vol. i., pp. 233,
280, 378). The harlequin duck
takes three years (ibid., vol.
iii., p. 614). The male of the
gold pheasant, as I hear from
Mr. Jenner Weir, can be distinguished
from the female when about three
months old, but he does not acquire
his full splendour until the
end of the September in the following
year.
*(2) Thus the Ibis tantalus
and Grus americanus take four
years, the flamingo several years,
and the Ardea ludovicana two
years, before they acquire their
perfect plumage. See Audubon,
ibid., vol. i., p. 221; vol.
iii., pp. 133, 139, 211.
With birds it
is difficult to decide by what
standard we ought
to judge of the earliness or
lateness of the period of variation,
whether by the age in reference
to the duration of life, or to
the power of reproduction, or
to the number of moults through
which the species passes. The
moulting of birds, even within
the same family, sometimes differs
much without any assignable cause.
Some birds moult so early, that
nearly all the body feathers
are cast off before the first
wing-feathers are fully grown;
and we cannot believe that this
was the primordial state of things.
When the period of moulting has
been accelerated, the age at
which the colours of the adult
plumage are first developed will
falsely appear to us to be earlier
than it really is. This may be
illustrated by the practice followed
by some bird-fanciers, who pull
out a few feathers from the breast
of nestling bullfinches, and
from the head or neck of young
gold-pheasants, in order to ascertain
their sex; for in the males,
these feathers are immediately
replaced by coloured ones.* The
actual duration of life is known
in but few birds, so that we
can hardly judge by this standard.
And, with reference to the period
at which the power of reproduction
is gained, it is a remarkable
fact that various birds occasionally
breed whilst retaining their
immature plumage.*(2) The fact
of birds breeding in their immature
plumage seems opposed to the
belief that sexual selection
has played as important a part,
as I believe it has, in giving
ornamental colours, plumes, &c.,
to the males, and, by means of
equal transmission, to the females
of many species. The objection
would be a valid one, if the
younger and less ornamental males
were as successful in winning
females and propagating their
kind, as the older and more beautiful
males. But we have no reason
to suppose that this is the case.
Audubon speaks of the breeding
of the immature males of Ibis
tantalus as a rare event, as
does Mr. Swinhoe, in regard to
the immature males of Oriolus.*(3)
If the young of any species in
their immature plumage were more
successful in winning partners
than the adults, the adult plumage
would probably soon be lost,
as the males would prevail, which
retained their immature dress
for the longest period, and thus
the character of the species
would ultimately be modified.*(4)
If, on the other hand, the young
never succeeded in obtaining
a female, the habit of early
reproduction would perhaps be
sooner or later eliminated, from
being superfluous and entailing
waste of power.
* Mr. Blyth, in Charlesworth's
Magazine of Natural History,
vol. i., 1837, p. 300. Mr. Bartlett
has informed me in regard to
gold pheasants.
*(2) I have noticed the following
cases in Audubon's Ornith. Biography.
The red-start of America (Muscapica
ruticilla, vol. i., p. 203).
The Ibis tantalus takes four
years to come to full maturity,
but sometimes breeds in the second
year (vol. iii., p. 133). The
Grus americanus takes the same
time, but breeds before acquiring
its full plumage (vol. iii.,
p. 211). The adults of Ardea
caerulea are blue, and the young
white; and white, mottled, and
mature blue birds may all be
seen breeding together (vol.
iv., p. 58): but Mr. Blyth informs
me that certain herons apparently
are dimorphic, for white and
coloured individuals of the same
age may be observed. The harlequin
duck (Anas histrionica, Linn.)
takes three years to acquire
its full plumage, though many
birds breed in the second year
(vol. iii., p. 614). The white-beaded
eagle (Falco leucocephalus, vol.
iii., p. 210) is likewise known
to breed in its immature state.
Some species of Oriolus (according
to Mr. Blyth and Mr. Swinhoe,
in Ibis, July, 1863, p. 68) likewise
breed before they attain their
full plumage.
*(3) See the last footnote.
*(4) Other animals, belonging
to quite distinct classes, are
either habitually or occasionally
capable of breeding before they
have fully acquired their adult
characters. This is the case
with the young males of the salmon.
Several amphibians have been
known to breed whilst retaining
their larval structure. Fritz
Muller has shewn (Facts and Arguments
for Darwin, Eng. trans., 1869,
p. 79) that the males of several
amphipod crustaceans become sexually
mature whilst young; and I infer
that this is a case of premature
breeding, because they have not
as yet acquired their fully-developed
claspers. All such facts are
highly interesting, as bearing
on one means by which species
may undergo great modifications
of character.
The plumage of certain birds
goes on increasing in beauty
during many years after they
are fully mature; this is the
case with the train of the peacock,
with some of the birds of paradise,
and with the crest and plumes
of certain herons, for instance,
the Ardea ludovicana.* But it
is doubtful whether the continued
development of such feathers
is the result of the selection
of successive beneficial variations
(though this is the most probable
view with birds of paradise)
or merely of continuous growth.
Most fishes continue increasing
in size, as long as they are
in good health and have plenty
of food; and a somewhat similar
law may prevail with the plumes
of birds.
* Jerdon, Birds of India, vol.
iii., p. 507, on the peacock.
Dr. Marshall thinks that the
older and more brilliant males
of birds of paradise, have an
advantage over the younger males;
see Archives Neerlandaises, tom.
vi., 1871.- On Ardea, Audubon,
ibid., vol. iii., p. 139.
CLASS V When the adults of both
sexes have a distinct winter
and summer plumage, whether or
not the male differs from the
female, the young resemble the
adults of both sexes in their
winter dress, or much more rarely
in their summer dress, or they
resemble the females alone. Or
the young may have an intermediate
character; or, again, they may
differ greatly from the adults
in both their seasonal plumages.-
The cases in this class are singularly
complex; nor is this surprising,
as they depend on inheritance,
limited in a greater or less
degree in three different ways,
namely, by sex, age, and the
season of the year. In some cases
the individuals of the same species
pass through at least five distinct
states of plumage. With the species,
in which the male differs from
the female during the summer
season alone, or, which is rarer,
during both seasons,* the young
generally resemble the females,-
as with the so-called gold-finch
of North America, and apparently
with the splendid Maluri of Australia.*(2)
With these species, the sexes
of which are alike during both
the summer and winter, the young
may resemble the adults, firstly,
in their winter dress; secondly,
and this is of much rarer occurrence,
in their summer dress; thirdly,
they may be intermediate between
these two states; and, fourthly,
they may differ greatly from
the adults at all seasons. We
have an instance of the first
of these four cases in one of
the egrets of India (Buphus coromandus),
in which the young and the adults
of both sexes are white during
the winter, the adults becoming
golden-buff during the summer.
* For illustrative
cases, see vol. iv. of Macgillivray's
History
of British Birds; on Tringa, &c.,
pp. 229, 271; on the Machetes,
p. 172; on the Charadrius hiaticula,
p. 118; on the Charadrius pluvialis,
p. 94.
*(2) For the goldfinch of N.
America, Fringilla tristis, Linn.,
see Audubon, Ornithological Biography
vol. i., p. 172. For the Maluri,
Gould's Handbook of the Birds
of Australia, vol. i., p. 318.
With the gaper (Anastomus oscitans)
of India we have a similar case,
but the colours are reversed:
for the young and the adults
of both sexes are grey and black
during the winter, the adults
becoming white during the summer.*
As an instance of the second
case, the young of the razor-bill
(Alca torda, Linn.), in an early
state of plumage, are coloured
like the adults during the summer;
and the young of the white-crowned
sparrow of North America (Fringilla
leucophrys), as soon as fledged,
have elegant white stripes on
their heads, which are lost by
the young and the old during
the winter.*(2) With respect
to the third case, namely, that
of the young having an intermediate
character between the summer
and winter adult plumages, Yarrell*(3)
insists that this occurs with
many waders. Lastly, in regard
to the young differing greatly
from both sexes in their adult
summer and winter plumages, this
occurs with some herons and egrets
of North America and India,-
the young alone being white.
* I am indebted to Mr. Blyth
for information as to the Buphus;
see also Jerdon, Birds of India,
vol. iii., p. 749. On the Anastomus,
see Blyth, in Ibis, 1867, p.
173.
*(2) On the Alca, see Macgillivray,
Hist. Brit. Birds, vol. v., p.
347. On the Fringilla leucophrys,
Audubon, ibid., vol. ii., p.
89. I shall have hereafter to
refer to the young of certain
herons and egrets being white.
*(3) History of British Birds,
vol. i., 1839, p. 159.
I will make only a few remarks
on these complicated cases. When
the young resemble the females
in their summer dress, or the
adults of both sexes in their
winter dress, the cases differ
from those given under Classes
I and Ill only in the characters
originally acquired by the males
during the breeding-season, having
been limited in their transmission
to the corresponding season.
When the adults have a distinct
summer and winter plumage, and
the young differ from both, the
case is more difficult to understand.
We may admit as probable that
the young have retained an ancient
state of plumage; we can account
by sexual selection for the summer
or nuptial plumage of the adults,
but how are we to account for
their distinct winter plumage?
If we could admit that this plumage
serves in all cases as a protection,
its acquirement would be a simple
affair; but there seems no good
reason for this admission. It
may be suggested that the widely
different conditions of life
during the winter and summer
have acted in a direct manner
on the plumage; this may have
had some effect, but I have not
much confidence in so great a
difference as we sometimes see
between the two plumages, having
been thus caused. A more probable
explanation is, that an ancient
style of plumage, partially modified
through the transference of some
characters from the summer plumage,
has been retained by the adults
during the winter. Finally, all
the cases in our present class
apparently depend on characters
acquired by the adult males,
having been variously limited
in their transmission according
to age, season, and sex; but
it would not be worth while to
attempt to follow out these complex
relations.
CLASS VI The young in their
first plumage differ from each
other according to sex; the young
males resembling more or less
closely the adult males, and
the young females more or less
closely the adult females.- The
cases in the present class, though
occurring in various groups,
are not numerous; yet it seems
the most natural thing that the
young should at first somewhat
resemble the adults of the same
sex, and gradually become more
and more like them. The adult
male blackcap (Sylvia atricapilla)
has a black head, that of the
female being reddish-brown; and
I am informed by Mr. Blyth, that
the young of both sexes can be
distinguished by this character
even as nestlings. In the family
of thrushes an unusual number
of similar cases have been noticed;
thus, the male blackbird (Turdus
merula) can be distinguished
in the nest from the female.
The two sexes of the mocking
bird (Turdus polyglottus, Linn.)
differ very little from each
other, yet the males can easily
be distinguished at a very early
age from the females by showing
more pure white.* The males of
a forest-thrush and of a rock-thrush
(Orocetes erythrogastra and Petrocincla
cyanea) have much of their plumage
of a fine blue, whilst the females
are brown; and the nestling males
of both species have their main
wing and tail-feathers edged
with blue whilst those of the
female are edged with brown.*(2)
In the young blackbird the wing-feathers
assume their mature character
and become black after the others;
on the other hand, in the two
species just named the wing-feather
become blue before the others.
The most probable view with reference
to the cases in the present class
is that the males, differently
from what occurs in Class I,
have transmitted their colours
to their male offspring at an
earlier age than that at which
they were first acquired; for,
if the males had varied whilst
quite young, their characters
would probably have been transmitted
to both sexes.*(3)
* Audubon, Ornith. Biography,
vol. i., p. 113.
*(2) Mr. C. A. Wright, in Ibis,
vol. vi., 1864, p. 65. Jerdon,
Birds of India, vol. i., p. 515.
See also on the blackbird, Blyth
in Charlesworth's Magazine of
Natural History, vol. i., 1837,
p. 113.
*(3) The following additional
cases may be mentioned; the young
males of Tanagra rubra can be
distinguished from the young
females (Audubon, Ornith. Biography,
vol. iv., p. 392), and so it
is within the nestlings of a
blue nuthatch, Dendrophila frontalis
of India (Jerdon, Birds of India,
vol. i., p. 389). Mr, Blyth also
informs me that the sexes of
the stonechat, Saxicola rubicola,
are distinguishable at a very
early age. Mr. Salvin gives (Proc.
Zoolog. Soc., 1870, p. 206) the
case of a humming-bird, like
the following one of Eustephanus.
In Aithurus polytmus, a humming-bird,
the male is splendidly coloured
black and green, and two of the
tail-feathers are immensely lengthened;
the female has an ordinary tail
and inconspicuous colours; now
the young males, instead of resembling
the adult female, in accordance
with the common rule, begin from
the first to assume the colours
proper to their sex, and their
tail-feathers soon become elongated.
I owe this information to Mr.
Gould, who has given me the following
more striking and as yet unpublished
case. Two humming-birds belonging
to the genus Eustephanus, both
beautifully coloured, inhabit
the small island of Juan Fernandez,
and have always been ranked as
specifically distinct. But it
has lately been ascertained that
the one which is of a rich chestnut-brown
colour with a golden-red head,
is the male, whilst the other
which is elegantly variegated
with green and white with a metallic
green head is the female. Now
the young from the first somewhat
resemble the adults of the corresponding
sex, the resemblance gradually
becoming more and more complete.
In considering this last case,
if as before we take the plumage
of the young as our guide, it
would appear that both sexes
have been rendered beautiful
independently; and not that one
sex has partially transferred
its beauty to the other. The
male apparently has acquired
his bright colours through sexual
selection in the same manner
as, for instance, the peacock
or pheasant in our first class
of cases; and the female in the
same manner as the female Rhynchaea
or Turnix in our second class
of cases. But there is much difficulty
in understanding how this could
have been effected at the same
time with the two sexes of the
same species. Mr. Salvin states,
as we have seen in the eighth
chapter, that with certain humming-birds
the males greatly exceed the
females in number, whilst with
other species inhabiting the
same country the females greatly
exceed the males. If, then, we
might assume that during some
former lengthened period the
males of the Juan Fernandez species
had greatly exceeded the females
in number, but that during another
lengthened period the females
had far exceeded the males, we
could understand how the males
at one time, and the females
at another, might have been rendered
beautiful by the selection of
the brighter coloured individuals
of either sex; both sexes transmitting
their characters to their young
at a rather earlier age than
usual. Whether this is the true
explanation I will not pretend
to say; but the case is too remarkable
to be passed over without notice.
We have now seen in all six
classes, that an intimate relation
exists between the plumage of
the young and the adults, either
of one sex or both. These relations
are fairly well explained on
the principle that one sex- this
being in the great majority of
cases the male- first acquired
through variation and sexual
selection bright colours or other
ornaments, and transmitted them
in various ways, in accordance
with the recognised laws of inheritance.
Why variations have occurred
at different periods of life,
even sometimes with species of
the same group, we do not know,
but with respect to the form
of transmission, one important
determining cause seems to be
the age at which the variations
first appear.
From the principle of inheritance
at corresponding ages, and from
any variations in colour which
occurred in the males at an early
age not being then selected-
on the contrary being often eliminated
as dangerous- whilst similar
variations occurring at or near
the period of reproduction have
been preserved, it follows that
the plumage of the young will
often have been left unmodified,
or but little modified. We thus
get some insight into the colouring
of the progenitors of our existing
species. In a vast number of
species in five out of our six
classes of cases, the adults
of one sex or of both are bright
coloured, at least during the
breeding-season, whilst the young
are invariably less brightly
coloured than the adults, or
are quite dull coloured; for
no instance is known, as far
as I can discover, of the young
of dull-coloured species displaying
bright colours, or of the young
of bright-coloured species being
more brilliant than their parents.
In the fourth class, however,
in which the young and the old
resemble each other, there are
many species (though by no means
all), of which the young are
bright-coloured, and as these
form old groups, we may infer
that their early progenitors
were likewise bright. With this
exception, if we look to the
birds of the world, it appears
that their beauty has been much
increased since that period,
of which their immature plumage
gives us a partial record.
On the Colour
of the Plumage in relation
to Protection.- It
will have been seen that I cannot
follow Mr. Wallace in the belief
that dull colours, when confined
to the females, have been in
most cases specially gained for
the sake of protection. There
can, however, be no doubt, as
formerly remarked, that both
sexes of many birds have had
their colours modified, so as
to escape the notice of their
enemies; or in some instances,
so as to approach their prey
unobserved, just as owls have
had their plumage rendered soft,
that their flight may not be
overheard. Mr. Wallace remarks*
that "it is only in the tropics,
among forests which never lose
their foliage, that we find whole
groups of birds, whose chief
colour is green." It will be
admitted by every one, who has
ever tried, how difficult it
is to distinguish parrots in
a leaf-covered tree. Nevertheless,
we must remember that many parrots
are ornamented with crimson,
blue, and orange tints, which
can hardly be protective. Woodpeckers
are eminently arboreal, but besides
green species, there are many
black, and black-and-white kinds-
all the species being apparently
exposed to nearly the same dangers.
It is therefore probable that
with tree-haunting birds, strongly-pronounced
colours have been acquired through
sexual selection, but that a
green tint has been acquired
oftener than any other, from
the additional advantage of protection.
* Westminster Review, July,
1867, p. 5.
In regard to
birds which live on the ground,
every one admits
that they are coloured so as
to imitate the surrounding surface.
How difficult it is to see a
partridge, snipe, woodcock, certain
plovers, larks, and night-jars
when crouched on ground. Animals
inhabiting deserts offer the
most striking cases, for the
bare surface affords no concealment,
and nearly all the smaller quadrupeds,
reptiles, and birds depend for
safety on their colours. Mr.
Tristram has remarked in regard
to the inhabitants of the Sahara,
that all are protected by their "isabelline
or sand-colour."* Calling to
my recollection the desert-birds
of South America, as well as
most of the ground-birds of Great
Britain, it appeared to me that
both sexes in such cases are
generally coloured nearly alike.
Accordingly, I applied to Mr.
Tristram with respect to the
birds of the Sahara, and he has
kindly given me the following
information. There are twenty-six
species belonging to fifteen
genera, which manifestly have
their plumage coloured in a protective
manner; and this colouring is
all the more striking, as with
most of these birds it differs
from that of their congeners.
Both sexes of thirteen out of
the twenty-six species are coloured
in the same manner; but these
belong to genera in which this
rule commonly prevails, so that
they tell us nothing about the
protective colours being the
same in both sexes of desert-birds.
Of the other thirteen species,
three belong to genera in which
the sexes usually differ from
each other, yet here they have
the sexes alike. In the remaining
ten species, the male differs
from the female; but the difference
is confined chiefly to the under
surface of the plumage, which
is concealed when the bird crouches
on the ground; the head and back
being of the same sand-coloured
hue in the two sexes. So that
in these ten species the upper
surfaces of both sexes have been
acted on and rendered alike,
through natural selection, for
the sake of protection; whilst
the lower surfaces of the males
alone have been diversified,
through sexual selection, for
the sake of ornament. Here, as
both sexes are equally well protected,
we clearly see that the females
have not been prevented by natural
selection from inheriting the
colours of their male parents;
so that we must look to the law
of sexually-limited transmission.
* Ibis, 1859, vol. i., p. 429,
et seq. Dr. Rohlfs, however,
remarks to me in a letter that
according to his experience of
the Sahara, this statement is
too strong.
In all parts of the world both
sexes of many soft-billed birds,
especially those which frequent
reeds or sedges, are obscurely
coloured. No doubt if their colours
had been brilliant, they would
have been much more conspicuous
to their enemies; but whether
their dull tints have been specially
gained for the sake of protection
seems, as far as I can judge,
rather doubtful. It is still
more doubtful whether such dull
tints can have been gained for
the sake of ornament. We must,
however, bear in mind that male
birds, though dull-coloured,
often differ much from their
females (as with the common sparrow),
and this leads to the belief
that such colours have been gained
through sexual selection, from
being attractive. Many of the
soft-billed birds are songsters;
and a discussion in a former
chapter should not be forgotten,
in which it was shewn that the
best songsters are rarely ornamented
with bright tints. It would appear
that female birds, as a general
rule, have selected their mates
either for their sweet voices
or gay colours, but not for both
charms combined. Some species,
which are manifestly coloured
for the sake of protection, such
as the jack-snipe, woodcock,
and night-jar, are likewise marked
and shaded, according to our
standard of taste, with extreme
elegance. In such cases we may
conclude that both natural and
sexual selection have acted conjointly
for protection and ornament.
Whether any bird exists which
does not possess some special
attraction, by which to charm
the opposite sex, may be doubted.
When both sexes are so obscurely
coloured that it would be rash
to assume the agency of sexual
selection, and when no direct
evidence can be advanced shewing
that such colours serve as a
protection, it is best to own
complete ignorance of the cause,
or, which comes to nearly the
same thing, to attribute the
result to the direct action of
the conditions of life.
Both sexes of
many birds are conspicuously,
though not brilliantly
coloured, such as the numerous
black, white, or piebald species;
and these colours are probably
the result of sexual selection.
With the common blackbird, capercailzie,
blackcock, black scoter-duck
(Oidemia), and even with one
of the birds of paradise (Lophorina
atra), the males alone are black,
whilst the females are brown
or mottled; and there can hardly
be a doubt that blackness in
these cases has been a sexually
selected character. Therefore
it is in some degree probable
that the complete or partial
blackness of both sexes in such
birds as crows, certain cockatoos,
storks, and swans, and many marine
birds, is likewise the result
of sexual selection, accompanied
by equal transmission to both
sexes; for blackness can hardly
serve in any case as a protection.
With several birds, in which
the male alone is black, and
in others in which both sexes
are black, the beak or skin about
the head is brightly coloured,
and the contrast thus afforded
adds much to their beauty; we
see this in the bright yellow
beak of the male blackbird, in
the crimson skin over the eyes
of the blackcock and capercailzie,
in the brightly and variously
coloured beak of the scoter-drake
(Oidemia), in the red beak of
the chough (Corvus graculus,
Linn.), of the black swan, and
the black stork. This leads me
to remark that it is not incredible
that toucans may owe the enormous
size of their beaks to sexual
selection, for the sake of displaying
the diversified and vivid stripes
of colour, with which these organs
are ornamented.* The naked skin,
also, at the base of the beak
and round the eyes is likewise
often brilliantly coloured; and
Mr. Gould, in speaking of one
species,*(2) Says that the colours
of the beak "are doubtless in
the finest and most brilliant
state during the time of pairing." There
is no greater improbability that
toucans should be encumbered
with immense beaks, though rendered
as light as possible by their
cancellated structure, for the
display of fine colours (an object
falsely appearing to us unimportant),
than that the male Argus pheasant
and some other birds should be
encumbered with plumes so long
as to impede their flight.
* No satisfactory
explanation has ever been offered
of the
immense size, and still less
of the bright colours, of the
toucan's beak. Mr. Bates (The
Naturalist on the Amazons, vol.
ii., 1863, p. 341) states that
they use their beaks for reaching
fruit at the extreme tips of
the branches; and likewise, as
stated by other authors, for
extracting eggs and young birds
from the nests of other birds.
But, as Mr. Bates admits, the
beak "can scarcely be considered
a very perfectly-formed instrument
for the end to which it is applied." The
great bulk of the beak, as shown
by its breadth, depth, as well
as length, is not intelligible
on the view that it serves merely
as an organ of prehension. Mr.
Belt believes (The Naturalist
in Nicaragua, p. 197) that the
principal use of the beak is
as a defence against enemies,
especially to the female whilst
nesting in a hole in a tree.
*(2) Rhamphastos carinatus,
Gould's Monograph of Ramphastidae.
In the same
manner, as the males alone
of various species
are black, the females being
dull-coloured; so in a few cases
the males alone are either wholly
or partially white, as with the
several bell-birds of South America
(Chasmorhynchus), the Antarctic
goose (Bernicla antarctica),
the silver pheasant, &c., whilst
the females are brown or obscurely
mottled. Therefore, on the same
principle as before, it is probable
that both sexes of many birds,
such as white cockatoos, several
egrets with their beautiful plumes,
certain ibises, gulls, terns, &c.,
have acquired their more or less
completely white plumage through
sexual selection. In some of
these cases the plumage becomes
white only at maturity. This
is the case with certain gannets,
tropic-birds, &c., and with the
snow-goose (Anser hyperboreus).
As the latter breeds on the "barren
grounds," when not covered with
snow, and as it migrates southward
during the winter, there is no
reason to suppose that its snow-white
adult plumage serves as a protection.
In the Anastomus oscitans, we
have still better evidence that
the white plumage is nuptial
character, for it is developed
only during the summer; the young
in their immature state, and
the adults in their winter dress,
being grey and black. With many
kinds of gulls (Larus), the head
and neck become pure white during
the summer, being grey or mottled
during the winter and in the
young state. On the other hand,
with the smaller gulls, or sea-mews
(Gavia), and with some terns
(Sterna), exactly the reverse
occurs; for the heads of the
young birds during the first
year, and of the adults during
the winter, are either pure white,
or much paler coloured than during
the breeding-season. These latter
cases offer another instance
of the capricious manner in which
sexual selection appears often
to have acted.*
* On Larus, Gavia, and Sterna,
see Macgillivray, History of
British Birds, vol. v., pp. 515,
584, 626. On the Anser hyperboreus,
Audubon, Ornithological Biography,
vol. iv., p. 562. On the Anastomus,
Mr. Blyth, in Ibis, 1867, p.
173.
That aquatic birds have acquired
a white plumage so much oftener
than terrestrial birds, probably
depends on their large size and
strong powers of flight, so that
they can easily defend themselves
or escape from birds of prey,
to which moreover they are not
much exposed. Consequently, sexual
selection has not here been interfered
with or guided for the sake of
protection. No doubt with birds
which roam over the open ocean,
the males and females could find
each other much more easily,
when made conspicuous either
by being perfectly white or intensely
black; so that these colours
may possible serve the same end
as the call-notes of many land-birds.*
A white or black bird when it
discovers and flies down to a
carcase floating on the sea or
cast up on the beach, will be
seen from a great distance, and
will guide other birds of the
same and other species, to the
prey; but as this would be a
disadvantage to the first finders,
the individuals which were the
whitest or blackest would not
thus procure more food than the
less strongly coloured individuals.
Hence conspicuous colours cannot
have been gradually acquired
for this purpose through natural
selection.
* It may be noticed that with
vultures, which roam far and
wide high in the air, like marine
birds over the ocean, three or
four species are almost wholly
or largely white, and that many
others are black. So that here
again conspicuous colours may
possibly aid the sexes in finding
each other during the breeding-season.
As sexual selection depends
on so fluctuating an element
as taste, we can understand how
it is that, within the same group
of birds having nearly the same
habits, there should exist white
or nearly white, as well as black,
or nearly black species,- for
instance, both white and black
cockatoos, storks, ibises, swans,
terns, and petrels. Piebald birds
likewise sometimes occur in the
same groups together with black
and white species; for instance,
the black-necked swan, certain
terns, and the common magpie.
That a strong contrast in colour
is agreeable to birds, we may
conclude by looking through any
large collection, for the sexes
often differ from each other
in the male having the pale parts
of a purer white, and the variously
coloured dark parts of still
darker tints than the female.
It would even
appear that mere novelty, or
slight changes for
the sake of change, have sometimes
acted on female birds as a charm,
like changes of fashion with
us. Thus the males of some parrots
can hardly be said to be more
beautiful than the females, at
least according to our taste,
but they differ in such points,
as in having a rose-coloured
collar instead of "a bright emeraldine
narrow green collar"; or in the
male having a black collar instead
of "a yellow demi-collar in front," with
a pale roseate instead of a plum-blue
head.* As so many male birds
have elongated tail-feathers
or elongated crests for their
chief ornament, the shortened
tail, formerly described in the
male of a humming-bird, and the
shortened crest of the male goosander,
seem like one of the many changes
of fashion which we admire in
our own dresses.
* See Jerdon on the genus Palaeornis,
Birds of India, vol. i., pp.
258-260.
Some members of the heron family
offer a still more curious case
of novelty in colouring having,
as it appears, been appreciated
for the sake of novelty. The
young of the Ardea asha are white,
the adults being dark slate-coloured;
and not only the young, but the
adults in their winter plumage,
of the allied Buphus coromandus
are white, this colour changing
into a rich golden-buff during
the breeding-season. It is incredible
that the young of these two species,
as well as of some other members
of the same family,* should for
any special purpose have been
rendered pure white and thus
made conspicuous to their enemies;
or that the adults of one of
these two species should have
been specially rendered white
during the winter in a country
which is never covered with snow.
On the other hand we have good
reason to believe that whiteness
has been gained by many birds
as a sexual ornament. We may
therefore conclude that some
early progenitor of the Ardea
asha and the Buphus acquired
a white plumage for nuptial purposes,
and transmitted this colour to
their young; so that the young
and the old became white like
certain existing egrets; and
that the whiteness was afterwards
retained by the young, whilst
it was exchanged by the adults
for more strongly-pronounced
tints. But if we could look still
further back to the still earlier
progenitors of these two species,
we should probably see the adults
dark-coloured. I infer that this
would be the case, from the analogy
of many other birds, which are
dark whilst young, and when adult
are white; and more especially
from the case of the Ardea gularis,
the colours of which are the
reverse of those of A. asha,
for the young are dark-coloured
and the adults white, the young
having retained a former state
of plumage. It appears therefore
that, during a long line of descent,
the adult progenitors of the
Ardea asha, the Buphus, and of
some allies, have undergone the
following changes of colour:
first, a dark shade; secondly,
pure white; and thirdly, owing
to another change of fashion
(if I may so express myself),
their present slaty reddish,
or golden-buff tints. These successive
changes are intelligible only
on the principle of novelty having
been admired by birds for its
own sake.
* The young
of Ardea rufescens and A. caerulea
of the United
States are likewise white, the
adults being coloured in accordance
with their specific names. Audubon
(Ornithological Biography, vol.
iii., p. 416; vol. iv., p. 58)
seems rather pleased at the thought
that this remarkable change of
plumage will greatly "disconcert
the systematists."
Several writers
have objected to the whole
theory of sexual
selection, by assuming that with
animals and savages the taste
of the female for certain colours
or other ornaments would not
remain constant for many generations;
that first one colour and then
another would be admired, and
consequently that no permanent
effect could be produced. We
may admit that taste is fluctuating,
but it is not quite arbitrary.
It depends much on habit, as
we see in mankind; and we may
infer that this would hold good
with birds and other animals.
Even in our own dress, the general
character lasts long, and the
changes are to a certain extent
graduated. Abundant evidence
will be given in two places in
a future chapter, that savages
of many races have admired for
many generations the same cicatrices
on the skin, the same hideously
perforated lips, nostrils, or
ears, distorted heads, &c.; and
these deformities present some
analogy to the natural ornaments
of various animals. Nevertheless,
with savages such fashions do
not endure for ever, as we may
infer from the differences in
this respect between allied tribes
on the same continent. So again
the raisers of fancy animals
certainly have admired for many
generations and still admire
the same breeds; they earnestly
desire slight changes, which
are considered as improvements,
but any great or sudden change
is looked at as the greatest
blemish. With birds in a state
of nature we have no reason to
suppose that they would admire
an entirely new style of colouration,
even if great and sudden variations
often occurred, which is far
from being the case. We know
that dovecot pigeons do not willingly
associate with the variously
coloured fancy breeds; that albino
birds do not commonly get partners
in marriage; and that the black
ravens of the Feroe Islands chase
away their piebald brethren.
But this dislike of a sudden
change would not preclude their
appreciating slight changes,
any more than it does in the
case of man. Hence with respect
to taste, which depends on many
elements, but partly on habit
and partly on a love of novelty,
there seems no improbability
in animals admiring for a very
long period the same general
style of ornamentation or other
attractions, and yet appreciating
slight changes in colours, form,
or sound.
Summary of the Four Chapters
on Birds.- Most male birds are
highly pugnacious during the
breeding-season, and some possess
weapons adapted for fighting
with their rivals. But the most
pugnacious and the best armed
males rarely or never depend
for success solely on their power
to drive away or kill their rivals,
but have special means for charming
the female. With some it is the
power of song, or of giving forth
strange cries, or instrumental
music, and the males in consequence
differ from the females in their
vocal organs, or in the structure
of certain feathers. From the
curiously diversified means for
producing various sounds, we
gain a high idea of the importance
of this means of courtship. Many
birds endeavour to charm the
females by love-dances or antics,
performed on the ground or in
the air, and sometimes at prepared
places. But ornaments of many
kinds, the most brilliant tints,
combs and wattles, beautiful
plumes, elongated feathers, top-knots,
and so forth, are by far the
commonest means. In some cases
mere novelty appears to have
acted as a charm. The ornaments
of the males must be highly important
to them, for they have been acquired
in not a few cases at the cost
of increased danger from enemies,
and even at some loss of power
in fighting with their rivals.
The males of very many species
do not assume their ornamental
dress until they arrive at maturity,
or they assume it only during
the breeding-season, or the tints
then become more vivid. Certain
ornamental appendages become
enlarged, turgid, and brightly
coloured during the act of courtship.
The males display their charms
with elaborate care and to the
best effect; and this is done
in the presence of the females.
The courtship is sometimes a
prolonged affair, and many males
and females congregate at an
appointed place. To suppose that
the females do not appreciate
the beauty of the males, is to
admit that their splendid decorations,
all their pomp and display, are
useless; and this is incredible.
Birds have fine powers of discrimination,
and in some few instances it
can be shewn that they have a
taste for the beautiful. The
females, moreover, are known
occasionally to exhibit a marked
preference or antipathy for certain
individual males.
If it be admitted
that the females prefer, or
are unconsciously
excited by the more beautiful
males, then the males would slowly
but surely be rendered more and
more attractive through sexual
selection. That it is this sex
which has been chiefly modified,
we may infer from the fact that,
in almost every genus where the
sexes differ, the males differ
much more from one another than
do the females; this is well
shewn in certain closely-allied
representative species, in which
the females can hardly be distinguished,
whilst the males are quite distinct.
Birds in a state of nature offer
individual differences which
would amply suffice for the work
of sexual selection; but we have
seen that they occasionally present
more strongly marked variations
which recur so frequently that
they would immediately be fixed,
if they served to allure the
female. The laws of variation
must determine the nature of
the initial changes, and will
have largely influenced the final
result. The gradations, which
may be observed between the males
of allied species, indicate the
nature of the steps through which
they have passed. They explain
also in the most interesting
manner how certain characters
have originated, such as the
indented ocelli on the tail-feathers
of the peacock, and the ball-and-socket
ocelli on the wing-feathers of
the Argus pheasant. It is evident
that the brilliant colours, top-knots,
fine plumes, &c., of many male
birds cannot have been acquired
as a protection; indeed, they
sometimes lead to danger. That
they are not due to the direct
and definite action of the conditions
of life, we may feel assured,
because the females have been
exposed to the same conditions,
and yet often differ from the
males to an extreme degree. Although
it is probable that changed conditions
acting during a lengthened period
have in some cases produced a
definite effect on both sexes,
or sometimes on one sex alone,
the more important result will
have been an increased tendency
to vary or to present more strongly-marked
individual differences; and such
differences will have afforded
an excellent ground-work for
the action of sexual selection.
The laws of inheritance, irrespectively
of selection, appear to have
determined whether the characters
acquired by the males for the
sake of ornament, for producing
various sounds, and for fighting
together, have been transmitted
to the males alone or to both
sexes, either permanently, or
periodically during certain seasons
of the year. Why various characters
should have been transmitted
sometimes in one way and sometimes
in another, is not in most cases
known; but the period of variability
seems often to have been the
determining cause. When the two
sexes have inherited all characters
in common they necessarily resemble
each other; but as the successive
variations may be differently
transmitted, every possible gradation
may be found, even within the
same genus, from the closest
similarity to the widest dissimilarity
between the sexes. With many
closely-allied species, following
nearly the same habits of life,
the males have come to differ
from each other chiefly through
the action of sexual selection;
whilst the females have come
to differ chiefly from partaking
more or less of the characters
thus acquired by the males. The
effects, moreover, of the definite
action of the conditions of life,
will not have been masked in
the females, as in the males,
by the accumulation through sexual
selection of strongly-pronounced
colours and other ornaments.
The individuals of both sexes,
however affected, will have been
kept at each successive period
nearly uniform by the free intercrossing
of many individuals.
With species, in which the sexes
differ in colour, it is possible
or probable that some of the
successive variations often tended
to be transmitted equally to
both sexes; but that when this
occurred the females were prevented
from acquiring the bright colours
of the males, by the destruction
which they suffered during incubation.
There is no evidence that it
is possible by natural selection
to convert one form of transmission
into another. But there would
not be the least difficulty in
rendering a female dull-coloured,
the male being still kept bright-coloured,
by the selection of successive
variations, which were from the
first limited in their transmission
to the same sex. Whether the
females of many species have
actually been thus modified,
must at present remain doubtful.
When, through the law of the
equal transmission of characters
to both sexes, the females were
rendered as conspicuously coloured
as the males, their instincts
appear often to have been modified
so that they were led to build
domed or concealed nests.
In one small and curious class
of cases the characters and habits
of the two sexes have been completely
transposed, for the females are
larger, stronger, more vociferous
and brighter coloured than the
males. They have, also, become
so quarrelsome that they often
fight together for the possession
of the males, like the males
of other pugnacious species for
the possession of the females.
If, as seems probable, such females
habitually drive away their rivals,
and by the display of their bright
colours or other charms endeavour
to attract the males, we can
understand how it is that they
have gradually been rendered,
by sexual selection and sexually-limited
transmission, more beautiful
than the males- the latter being
left unmodified or only slightly
modified.
Whenever the law of inheritance
at corresponding ages prevails
but not that of sexually-limited
transmission, then if the parents
vary late in life- and we know
that this constantly occurs with
our poultry, and occasionally
with other birds- the young will
be left unaffected, whilst the
adults of both sexes will be
modified. If both these laws
of inheritance prevail and either
sex varies late in life, that
sex alone will be modified, the
other sex and the young being
unaffected. When variations in
brightness or in other conspicuous
characters occur early in life,
as no doubt often happens, they
will not be acted on through
sexual selection until the period
of reproduction arrives; consequently
if dangerous to the young, they
will be eliminated through natural
selection. Thus we can understand
how it is that variations arising
late in life have so often been
preserved for the ornamentation
of the males; the females and
the young being left almost unaffected,
and therefore like each other.
With species having a distinct
summer and winter plumage, the
males of which either resemble
or differ from the females during
both seasons or during the summer
alone, the degrees and kinds
of resemblance between the young
and the old are exceedingly complex;
and this complexity apparently
depends on characters, first
acquired by the males, being
transmitted in various ways and
degrees, as limited by age, sex,
and season.
As the young of so many species
have been but little modified
in colour and in other ornaments
we are enabled to form some judgment
with respect to the plumage of
their early progenitors; and
we may infer that the beauty
of our existing species, if we
look to the whole class, has
been largely increased since
that period, of which the immature
plumage gives us an indirect
record. Many birds, especially
those which live much on the
ground, have undoubtedly been
obscurely coloured for the sake
of protection. In some instances
the upper exposed surface of
the plumage has been thus coloured
in both sexes, whilst the lower
surface in the males alone has
been variously ornamented through
sexual selection. Finally, from
the facts given in these four
chapters, we may conclude that
weapons for battle, organs for
producing sound, ornaments of
many kinds, bright and conspicuous
colours, have generally been
acquired by the males through
variation and sexual selection,
and have been transmitted in
various ways according to the
several laws of inheritance-
the females and the young being
left comparatively but little
modified.*
* I am greatly indebted to the
kindness of Mr. Sclater for having
looked over these four chapters
on birds, and the two following
ones on mammals. In this way
I have been saved from making
mistakes about the names of the
species, and from stating anything
as a fact which is known to this
distinguished naturalist to be
erroneous. But, of course, he
is not at all answerable for
the accuracy of the statements
quoted by me from various authorities. |