Chapter X: Birds (2)

Similarly, a correspondent (Mr. J. Street) informs me of a case in which a pair of blackbirds, after having been disturbed by his gardener looking into their nest at their young, removed the latter to a distance of twenty yards, and deposited them in a more concealed place. Partridges are well known to do this, and similarly, according to Audubon, the goatsucker, when its nest is disturbed, removes its eggs to another place, the male and female both transporting eggs in their beaks.[165]

Still more curiously, a case is recorded in 'Comptes Rendu' (1836) of a pair of nightingales whose nest was threatened by a flood, and who transported it to a safe place, the male and the female bearing the nest between them.

Now, it is easy to see that if any particular bird is intelligent enough, as in the cases quoted, to perform this adjustive action of conveying young--whether to feeding-grounds, as in the case of the hen, or from sources of danger, as in the case of partridges, blackbirds, and goatsuckers--inheritance and natural selection might develop the originally intelligent adjustment into an instinct common to the species. And it so happens that this has actually occurred in at least two species of birds--viz., the woodcock and wild duck, both of which have been repeatedly observed to fly with their young upon their backs to and from their feeding-ground.

Couch gives some facts of interest relating to the mode of escape practised by the water-rail, swan, and some other aquatic birds. This consists in sinking under water, with only the bill remaining above the surface for respiration. When the swan has young, she may sink the head quite under water in order to allow the young to mount on it, and so be carried through even rapid currents.

The same author remarks that--

Many birds will carefully remove the meetings of the
young from the neighbourhood of their nests, in order
not to attract the attention of enemies; for while we
find that birds which make no secret of their
nesting-places are careless in such matters, the
woodpecker and the marsh tit in particular are at
pains to remove even the chips which are made in
excavating the cavities where the nests are placed,
and which might lead an observer to the sacred spot.

Similarly, Jesse observes:--

The excrement of the young of many birds who build
their nests without any pretensions to concealment,
such as the swallow, crow, &c., may at all times be
observed about or under the nest; while that of some
of those birds whose nests are more industriously
concealed is conveyed away in the mouths of the parent
birds, who generally drop it at a distance of twenty
or thirty yards from the nest. Were it not for this
precaution, the excrement itself, from its
accumulation, and commonly from its very colour, would
point out the place where the young were concealed.
When the young birds are ready to fly, or nearly so,
the old birds do not consider it any longer necessary
to remove the excrement.

Sir H. Davy gives an account of a pair of eagles which he saw on Ben Nevis teaching their young ones to fly; and every one must have observed the same thing among commoner species of birds. The experiments of Spalding, however, have shown that flying is an instinctive faculty; so that when he reared swallows from the nest and liberated them only after they were fully fledged, they flew well immediately on being liberated. Therefore, the 'teaching to fly' by parent birds must be regarded as mere encouragement to develop instinctive powers, which in virtue of this encouragement are probably developed sooner than would otherwise be the case.

A few observations may here be offered on some habits which do not fall under any particular heading.

The habit which many small birds display of mobbing carnivorous ones is probably due to a desire to drive off the enemy, and perhaps also to warn friends by the hubbub. It may therefore perhaps be regarded as a display of concerted action, of which, however, we shall have better evidence further on. I have seen a flock of common terns mob a pirate tern, which shows that this combined action may be directed as much against robbery as against murder. Couch says he has seen blackbirds mobbing a cat which was concealed in a bush, and here the motive would seem to be that of warning friends rather than that of driving away the enemy.

I have observed among the sea-gulls at the Zoological Gardens a curious habit, or mode of challenge. This consists in ostentatiously picking up a small twig or piece of wood, and throwing it down before the bird challenged, in the way that a glove used to be thrown down by the old knights. I observed this action performed repeatedly by several individuals of the glaucous and black-back species in the early spring-time of the year, and so it probably has some remote connection with the instinct of nest-building.

_Nidification._

In connection with the habits and instincts peculiar to certain species of birds, I may give a short account of the more remarkable kinds of nidification that are met with in this class of animals. As the account must necessarily be brief, I shall only mention the more interesting of the usual types.

Petrels and puffins make their nests in burrows which they excavate in the earth. The great sulphur mountain in Guadaloupe is described by Wasser as 'all bored like a rabbit warren with the holes that these imps (_i.e._ petrels) excavate.' In the case of the puffin it is the male that does the work of burrowing. He throws himself upon his back in the tunnel which he has made, and digs it longer and longer with his broad bill, while casting out the mould with his webbed feet. The burrow when finished has several twists and turns in it, and is about ten feet deep. If a rabbit burrow is available, the puffin saves himself the trouble of digging by taking possession of the one already made. The kingfisher and land-martin also make their nests in burrows.

Certain auks lay their single egg on the bare rock while the stone curlew and goatsucker deposit theirs on the bare soil, returning, however, year after year to the same spot. Ostriches scrape holes in the sand to serve as extemporised nests for their eggs promiscuously dropped, which are then buried by a light coating of sand, and incubated during the day by the sunbeams, and at night by the male bird. Sometimes a number of female ostriches deposit their eggs in a common nest, and then take the duty of incubation by turns. Similarly, gulls, sandpipers, plovers, &c., place their eggs in shallow pits hollowed out of the soil. The kingfisher makes a bed of undigested fish-bones ejected as pellets from her stomach, and 'some of the swifts secrete from their salivary glands a fluid which rapidly hardens as it dries on exposure to the air into a substance resembling isinglass, and thus furnish the "edible birds' nests" that are the delight of the Chinese epicures.'[166]

The house-martin builds its nest of clay, which it sticks upon the face of a wall, and renders more tenacious by working into it little bits of straw, splinters of wood, &c. According to Mr. Gilbert White:--

That this work may not, while it is soft and green,
pull itself down by its own weight, the provident
architect has prudence and forbearance enough not to
advance her work too fast; but by building only in the
morning, and by dedicating the rest of the day to food
and amusement, gives it sufficient time to dry and
harden. About half an inch seems a sufficient layer
for a day. Thus careful workmen, when they build mud
walls (informed at first perhaps by these little
birds), raise but a moderate layer at a time, and then
desist, lest the work should become top-heavy, and
ruined by its own weight. By this method, in about ten
or twelve days is formed a hemispheric nest, with a
small aperture towards the top, strong, compact, and
warm, and perfectly fitted for all the purposes for
which it was intended.

Other birds build in wood. The tomtit and the woodpecker excavate a hole in a tree, and carefully carry away the chips, so as not to give any indication of the whereabouts of their nests. Wilson says that the American woodpecker makes an excavation five feet in depth, of a tortuous form, to keep out wind and rain.

The orchard starling suspends its nest from the branches of a tree, and uses for its material tough kinds of grass, the blades of which it weaves together. Wilson found one of these blades to be thirteen inches long, and to be woven in and out thirty-four times.

We may next notice the weaver (_Ploceus textor_) and tailor (_Prinia_, _Orthotomus_, and _Sylvia_). The former intertwines slender leaves of grass so as to produce a web sufficiently substantial for the protection of its young. The tailor-birds sew together leaves wherewith to make their nests, using for the purpose cotton and thread where they can find it, and natural vegetable fibres where they cannot obtain artificial. Colonel Sykes says that he has found the threads thus used for sewing knotted at the ends.[167]

Forbes saw the tailor-bird of the East Indies constructing its nest, and observed it to choose a plant with large leaves, gather cotton which it regularly spun into a thread by means of its bill and claws, and then sew the leaves together, using its beak as a needle, or rather awl.

This instinct is rendered particularly interesting to evolutionists from the fact that it is exhibited by three distinct genera. For, as the instinct is so peculiar and unique, it is not likely to have originated independently in the three genera, but must be regarded as almost certainly derived from a common ancestral type--thus showing that an instinct may be perpetuated unaltered after the differentiation of structure has proceeded beyond a specific distinction. The genus _Sylvia_ inhabits Italy, the other two inhabit India. _Sylvia_ uses for thread spiders' web collected from the egg-pouches, which is stitched through holes made in the edges of leaves, presumably with the beak.

The baya bird of India 'hangs its pendulous dwelling from a projecting bough, twisting it with grass into a form somewhat resembling a bottle with a prolonged neck, the entrance being inverted, so as to baffle the approaches of its enemies, the tree snakes and other reptiles.'

Sir E. Tennent, from whom this account is taken, adds:--

The natives assert that the male bird carries
fire-flies to the nest, and fastens them to its sides
by particles of soft mud. Mr. Layard assures me that
although he has never succeeded in finding the
fire-fly, the nest of the male bird (for the female
occupies another during incubation) invariably
contains a patch of mud on each side of the perch.

Dr. Buchanan confirms the report of the natives here alluded to, and says:--

At night each of the habitations is lighted up by a
fire-fly stuck on the top with a bit of clay. The nest
consists of two rooms; sometimes there are three or
four fire-flies, and their blaze in the little cells
dazzles the eyes of the bats, which often kill the
young of these birds.

While this work is passing through the press I meet with the following, which appears to refer to some independent, and therefore corroborative observation concerning the above-stated fact, and in any case is worth adding, on account of the observation concerning the rats, which, if trustworthy, would furnish a sufficient reason for the instinct of the birds. The extract is taken from a letter to 'Nature' (xxiv., p. 165), published by Mr. H. A. Severn:

I have been informed on safe authority that the Indian
bottle-bird protects his nest at night by sticking
several of these glow-beetles around the entrance by
means of clay; and only a few days back an intimate
friend of my own was watching three rats on a roof
rafter of his bungalow when a glow-fly lodged very
close to them; the rats immediately scampered off.

The Talegallus of Australia is, in the opinion of Gould,--

Among the most important of the ornithological
novelties which the exploration of Western and
Southern Australia has unfolded to us, and this from
the circumstance of its not hatching its own eggs,
which, instead of being incubated in the usual way,
are deposited in mounds of mixed sand and herbage, and
there left for the heating of the mass to develop the
young, which, when accomplished, force their way
through the sides of the mound, and commence an active
life from the moment they see the light of day.[168]

Sir George Grey measured one of these mounds, and found it to be 'forty-five feet in circumference, and if rounded in proportion on the top (it being at the time unfinished) would have been full five feet high.' The heat round the eggs was taken to be 89°.

A curious aberration of the nest-building instinct is sometimes shown by certain birds--particularly the common wren--which consists in building a supernumerary nest. That is to say, after one nest is completed, another is begun and finished before the eggs are laid, and the first nest is not used, though sometimes it is used in preference to the second.

As showing at once the eccentricity which birds sometimes display in the choice of a site, and also the determination of certain birds to return to the same site in successive years, I may allude to the case published by Bingley, of a pair of swallows which built their nest upon the wings and body of a dead owl, which was hanging from the rafters of a barn, and so loosely as to sway about with every gust of wind. The owl with the nest upon it was placed as a curiosity in the museum of Sir Ashton Lever, and he directed that a shell should be hung upon the rafters in the place which had been previously occupied by the dead owl. Next year the swallows returned and constructed their new nest in the cavity of the shell.[169]

The following is quoted from Thompson's 'Passions of Animals,' p. 205:--

The sociable grosbeak of Africa is one of the few
instances of birds living in community and uniting in
constructing one huge nest for the whole society. L.
Valiant's account has been fully confirmed by other
travellers. He says: 'I observed on the way a tree
with an enormous nest of these birds, which I have
called republicans; and as soon as I arrived at my
camp I despatched a few men with a waggon to bring it
to me, that I might open and examine the hive. When it
arrived, I cut it in pieces with a hatchet, and saw
that the chief portion of the structure consisted of a
mass of Boshman's grass, without any mixture, but so
compact and firmly basketed together as to be
impenetrable to the rain. This is the commencement of
the structure, and each bird builds its particular
nest under this canopy. But the nests are formed only
beneath the eaves, the upper surface remaining void,
without, however, being useless; for as it has a
projecting rim, and is a little inclined, it serves to
let the water run off, and preserves each little
dwelling from the rain. Figure to yourself a huge
irregular sloping roof, all the eaves of which are
covered with nests, crowded one against another, and
you will have a tolerably accurate idea of these
singular edifices. Each individual nest is three or
four inches in diameter, which is sufficient for the
bird; but, as they are all in contact with one another
around the eaves, they appear to the eye to form but
one building, and are distinguishable from each other
only by a little external aperture which serves as an
entrance to the nest; and even this is sometimes
common to three different nests, one of which is
situated at the bottom and the other two at the sides.
This large nest, which was one of the most
considerable I had anywhere seen in the course of my
journey, contained 320 inhabited cells, which,
supposing a male and female to each, would form a
society of 640 individuals; but as these birds are
polygamous, such a calculation would not be exact.'

The following is quoted from Couch ('Illustrations of Instinct,' p. 227 _et seq._):--

Mr. Waterton says there is a peculiarity in the
nidification of the domestic swan too singular to be
passed over without notice. At the time it lays its
first egg the nest which it has prepared is of very
moderate size; but as incubation proceeds we see it
increase vastly in height and breadth. Every soft
material, such as pieces of grass and fragments of
sedges, is laid hold of by the sitting swan as they
float within her reach, and are added to the nest.
This work of accumulation is performed by her during
the entire period of incubation, be the weather wet or
dry, settled or unsettled; and it is perfectly
astonishing to see with what assiduity she plies her
work of aggrandisement to a nest already sufficient
in strength and size to answer every end. My swans
generally form their nest on an island quite above the
reach of a flood; and still the sitting bird never
appears satisfied with the quantity of materials which
are provided for her nest. I once gave her two huge
bundles of oaten straw, and she performed her work of
apparent supererogation by applying the whole of it to
her nest, already very large, and not exposed to
destruction had the weather become ever so rainy.

This same author continues:--

It is probable that this disposition to accumulation,
in its general bearing, has reference to heat rather
than the flood; but that the wild swan has a foresight
regarding danger, and a quick perception as to the
means of securing safety, appears from an instance
mentioned by Captain Parry, in his Northern voyage.
When everything was deeply involved in ice, the
voyagers were obliged to pay much attention to discern
whether they were travelling over water or land; but
some birds, which formed their nest at no great
distance from the ships, were under no mistake in so
important a matter; and when the thaw took place it
was seen that the nest was situated on an island in
the lake.

The following cases are likewise taken from Couch (_loc. cit._, p. 225):--

This swan was eighteen or nineteen years old, had
brought up many broods, and was highly valued by the
neighbours. She exhibited, some eight or nine years
past, one of the most remarkable powers of instinct
ever recorded. She was sitting on four or five eggs,
and was observed to be very busy in collecting weeds,
grasses, &c., to raise her nest; a farming man was
ordered to take down half a load of haulm, with which
she most industriously raised her nest and the eggs
two feet and a half; that very night there came down a
tremendous fall of rain, which flooded all the
malt-shops and did great damage. Man made no
preparation, the bird did; instinct prevailed over
reason. Her eggs were above, and only just above, the
water.

During the early part of the summer of 1835, a pair of
water-hens built their nest by the margin of the
ornamental pond at Bell's Hill, a piece of water of
considerable extent, and ordinarily fed by a spring
from the height above, but into which the contents of
another large pond can occasionally be admitted. This
was done while the female was sitting; and as the nest
had been built when the water level stood low, the
sudden influx of this large body of water from the
second pond caused a rise of several inches, so as to
threaten the speedy immersion and consequent
destruction of the eggs. This the birds seem to have
been aware of, and immediately took precautions
against so imminent a danger; for when the gardener,
upon whose veracity I can safely rely, seeing the
sudden rise of the water, went to look after the nest,
expecting to find it covered and the eggs destroyed,
or at least forsaken by the hen, he observed, whilst
at a distance, both birds busily engaged about the
brink where the nest was placed; and when near enough
he clearly perceived that they were adding, with all
possible despatch, fresh materials to raise the fabric
beyond the level of the increased contents of the
pond; and that the eggs had by some means been removed
from the nest by the birds, and were then deposited
upon the grass about a foot or more from the margin of
the water. He watched them for some time, and saw the
nest rapidly increase in height; but I regret to add
that he did not remain long enough, fearing he might
create alarm, to witness the interesting act of
replacing the eggs which must have been effected
shortly after; for, upon his return in less than an
hour, he found the hen quietly sitting upon them in
the newly raised nest. In a few days afterwards the
young were hatched, and, as usual, soon quitted the
nest and took to the water with their parents. The
nest was shown to me _in situ_ shortly after, and I
could then plainly discern the formation of the new
with the older part of the fabric.

We must not conclude these remarks on nidification without alluding to Mr. Wallace's chapters on the 'Philosophy of Birds' Nests,' in his work on 'Natural Selection.' This writer is inclined to suppose that birds do not build their nests distinctive of their various species by the teachings of hereditary instinct, but by the young birds intelligently observing the construction of the nests in which they are hatched, and purposely imitating this construction when in the following season they have occasion to build nests of their own. With reference to this theory it is only needful to say that it is antecedently improbable, and not well substantiated by facts. It is antecedently improbable because, when any habit has been continued for a number of generations--especially when the habit is of a peculiar and detailed character--the probability is that it has become instinctive; we should have almost as much reason to anticipate that the nest of the little crustacean _Podocerus_, or the cell of the hive-bee, is constructed by a process of conscious imitation, as that this is the case with the nests of birds. And this theory is not well substantiated by facts because, if the theory were true, we should expect considerable differences to be usually presented by nests of the same species. Unless the construction of the nest of any given species were regulated by a common instinct, numberless idiosyncratic peculiarities would necessarily require to arise, and there would only be a very general uniformity of type presented by the nests of the same species.

A more valuable contribution to the 'Philosophy of Birds' Nests' is furnished by this able naturalist when he directs attention to a certain general correlation between the form of the nest and the colour of the female. For, on reviewing the birds of the world, he certainly makes good the proposition that, as a general rule, liable however to frequent exceptions, dull-coloured females sit on open nests, while those that are conspicuously coloured sit in domed nests. But Mr. Darwin, in a careful review of all the evidence, clearly shows that this interesting fact is to be attributed, not, as Mr. Wallace supposed, to the colour of the female having been determined through natural selection by the form of the nest, but to the reverse process of the form of the nest having been determined by the colour of the female.[170]

Another general fact of interest connected with nidification must not be omitted. This is that the instincts of nidification, although not so variable as the theory of Mr. Wallace would require, are nevertheless highly plastic. The falcon, which usually builds on a cliff, has been known to lay its eggs on the ground in a marsh; the golden eagle sometimes builds in trees or on the ground, while the heron varies its site between trees, cliffs, and open fen.[171] Again, Audubon, in his 'Ornithological Biography,' gives many cases of conspicuous local variations in the nests of the same species in the northern and southern United States; and, as Mr. Wallace truly observes,--

Many facts have already been given which show that
birds do adapt their nests to the situations in which
they place them; and the adoption of eaves, chimneys,
and boxes by swallows, wrens, and many other birds,
shows that they are always ready to take advantage of
changed conditions. It is probable, therefore, that a
permanent change of climate would cause many birds to
modify the form or materials of their abode, so as
better to protect their young.[172]

In America the change of habits in this respect undergone by the house-swallow has been accomplished within the last three hundred years.

Closely connected, if not identical, with this fact is another, namely, that in some species which have been watched closely for a sufficient length of time, a steady improvement in the construction of nests has been observed. Thus C. G. Leroy, who filled the post of Ranger of Versailles about a century ago, and therefore had abundant opportunities of studying the habits of animals, wrote an essay on 'The Intelligence and Perfectibility of Animals from a Philosophical Point of View.' In this essay he has anticipated the American observer Wilson in noticing that the nests of young birds are distinctly inferior to those of older ones, both as regards their situation and construction. As we have here independent testimony of two good observers to a fact which in itself is not improbable, I think we may conclude that the nest-making instinct admits of being supplemented, at any rate in some birds, by the experience and intelligence of the individual. M. Pouchet has also recorded that he has found a decided improvement to have taken place in the nests of the swallows at Rouen during his own lifetime; and this accords with the anticipation of Leroy that if our observation extended over a sufficient length of time, and in a manner sufficiently close, we should find that the accumulation of intelligent improvements by individuals of successive generations would begin to tell upon the inherited instinct, so that all the nests in a given locality would attain to a higher grade of excellence.

Leroy also says that when swallows are hatched out too late to migrate with the older birds, the instinct of migration is not sufficiently imperative to induce them to undertake the journey by themselves. 'They perish, the victims of their ignorance, and of the tardy birth which made them unable to follow their parents.'

_Cuckoo._

Perhaps the strangest of the special instincts manifested by birds is that of the cuckoo laying its eggs in the nests of other birds. As the subject is an important one from several points of view, I shall consider it at some length.

It must first be observed that the parasitic habit in question is not practised by all species of the genus--the American cuckoo, for instance, being well known to build its nest and rear its young in the ordinary manner. The Australian species, however, manifests the same instinct as the European. The first observer of the habit practised by the European cuckoo was the illustrious Jenner, who published his account in the 'Philosophical Transactions.'[173] From this account the following is an extract:--

The cuckoo makes choice of the nests of a great
variety of small birds. I have known its eggs
entrusted to the care of the hedge-sparrow,
water-wagtail, titlark, yellowhammer, green linnet,
and winchat. Among these it generally selects the
three former, but shows a much greater partiality to
the hedge-sparrow than to any of the rest; therefore,
for the purpose of avoiding confusion, this bird only,
in the following account, will be considered as the
foster-parent of the cuckoo, except in instances which
are particularly specified.

When the hedge-sparrow has sat her usual time, and
disengaged the young cuckoo and some of her own
offspring from the shell,[174] her own young ones, and
any of her eggs that remain unhatched, are soon turned
out, the young cuckoo remaining possessor of the
nest, and sole object of her future care. The young
birds are not previously killed, nor are the eggs
demolished, but all are left to perish together,
either entangled about the bush which contains the
nest, or lying on the ground under it.

On June 18, 1787, I examined the nest of a
hedge-sparrow, which then contained a cuckoo's and
three hedge-sparrow's eggs. On inspecting it the day
following, I found the bird had hatched, but that the
nest now contained a young cuckoo and only one young
hedge-sparrow. The nest was placed so near the
extremity of a hedge, that I could distinctly see what
was going forward in it; and, to my astonishment, saw
the young cuckoo, though so newly hatched, in the act
of turning out the young hedge-sparrow.

The mode of accomplishing this was very curious. The
little animal, with the assistance of its rump and
wings, contrived to get the bird upon its back, and
making a lodgment for the burden by elevating its
elbows, clambered backward with it up the side of the
nest till it reached the top, when, resting for a
moment, it threw off its load with a jerk, and quite
disengaged it from the nest. It remained in this
situation a short time, feeling about with the
extremities of its wings, as if to be convinced
whether this business was properly executed, and then
dropped into the nest again. With these (the
extremities of its wings) I have often seen it
examine, as it were, an egg and nestling before it
began its operations; and the sensibility which these
parts appeared to possess seemed sufficiently to
compensate the want of sight, which as yet it was
destitute of. I afterwards put in an egg, and this by
a similar process was conveyed to the edge of the nest
and thrown out. These experiments I have since
repeated several times in different nests, and have
always found the young cuckoo disposed to act in the
same manner. In climbing up the nest it sometimes
drops its burden, and thus is foiled in its
endeavours; but after a little respite the work is
resumed, and goes on almost incessantly till it is
effected. It is wonderful to see the extraordinary
exertions of the young cuckoo, when it is two or three
days old, if a bird be put into the nest with it that
is too weighty for it to lift out. In this state it
seems ever restless and uneasy. But this disposition
for turning out its companions begins to decline from
the time it is two or three till it is about twelve
days old, when, as far as I have hitherto seen, it
ceases. Indeed, the disposition for throwing out the
egg appears to cease a few days sooner; for I have
frequently seen the young cuckoo, after it had been
hatched nine or ten days, remove a nestling that had
been placed in the nest with it, when it suffered an
egg, put there at the same time, to remain unmolested.
The singularity of its shape is well adapted to these
purposes; for, different from other newly hatched
birds, its back from the scapulæ downwards is very
broad, with a considerable depression in the middle.
This depression seems formed by nature for the design
of giving a more secure lodgment to the egg of the
hedge-sparrow, or its young one, when the young cuckoo
is employed in removing either of them from the nest.
When it is about twelve days old this cavity is quite
filled up, and then the back assumes the shape of
nestling birds in general. . . . The circumstance of the
young cuckoo being destined by nature to throw out the
young hedge-sparrows seems to account for the parent
cuckoo dropping her egg in the nests of birds so small
as those I have particularised. If she were to do this
in the nest of a bird which produced a large egg, and
consequently a large nestling, the young cuckoo would
probably find an insurmountable difficulty in solely
possessing the nest, as its exertions would be unequal
to the labour of turning out the young birds. (I have
known a case in which a hedge-sparrow sat upon a
cuckoo's egg and one of her own. Her own egg was
hatched five days before the cuckoo's, when the young
hedge-sparrow had gained such a superiority in size
that the young cuckoo had not powers sufficient to
lift it out of the nest till it was two days old, by
which time it had grown very considerably. This egg
was probably laid by the cuckoo several days after the
hedge-sparrow had begun to sit; and even in this case
it appears that its presence had created the
disturbance before alluded to, as all the
hedge-sparrow's eggs had gone except one.) . . . June
27, 1787.--Two cuckoos and a hedge-sparrow were
hatched in the same nest this morning; one hedge
sparrow's egg remained unhatched. In a few hours
after, a contest began between the cuckoos for the
possession of the nest, which continued undetermined
till the next afternoon; when one of them, which was
somewhat superior in size, turned out the other,
together with the young hedge-sparrow and the
unhatched egg. This contest was very remarkable. The
combatants alternately appeared to have the advantage,
as each carried the other several times nearly to the
top of the nest, and then sunk down again oppressed
with the weight of its burden; till at length, after
various efforts, the strongest prevailed, and was
afterwards brought up by the hedge-sparrows.

To what cause, then, may we attribute the
singularities of the cuckoo? May they not be owing to
the following circumstances,--the short residence this
bird is allowed to make in the country where it is
destined to propagate its species, and the call that
nature has upon it, during that short residence, to
produce a numerous progeny? The cuckoo's first
appearance here is about the middle of April, commonly
on the 17th. Its egg is not ready for incubation till
some weeks after its arrival, seldom before the middle
of May. A fortnight is taken up by the sitting bird in
hatching the egg. The young bird generally continues
three weeks in the nest before it flies, and the
foster-parents feed it more than five weeks after this
period; so that, if a cuckoo should be ready with an
egg much sooner than the time pointed out, not a
single nestling, even one of the earliest, would be
fit to provide for itself before its parent would be
instinctively directed to seek a new residence, and be
thus compelled to abandon its young one; for old
cuckoos take their final leave of this country the
first week in July.

Had nature allowed the cuckoo to have stayed here as
long as some other migrating birds, which produce a
single set of young ones (as the swift or nightingale,
for example), and had allowed her to have reared as
large a number as any bird is capable of bringing up
at one time, there might not have been sufficient to
have answered her purpose; but by sending the cuckoo
from one nest to another, she is reduced to the same
state as the bird whose nest we daily rob of an egg,
in which case the stimulus for incubation is
suspended.

A writer in 'Nature' (vol. v., p. 383; and vol. ix., p. 123), to whom Mr. Darwin refers in the latest edition of 'The Origin of Species' as an observer that Mr. Gould has found trustworthy, precisely confirms, from observations of his own, the above description of Jenner. So far, therefore, as the observations are common I shall not quote his statements; but the following additional matter is worth rendering:--

But what struck me most was this: the cuckoo was
perfectly naked, without a vestige of a feather or
even a hint of future feathers; its eyes were not yet
opened, and its neck seemed too weak to support the
weight of its head. The pipits (in whose nest the
young cuckoo was parasitic) had well-developed quills
on the wings and back, and had bright eyes partially
open; yet they seemed quite helpless under the
manipulations of the cuckoo, which looked a much less
developed creature. The cuckoo's legs, however,
seemed very muscular, and it appeared to feel about
with its wings, which were absolutely featherless, as
with hands--the 'spurious wing' (unusually large in
proportion) looking like a spread-out thumb. The most
singular thing of all was the direct purpose with
which the blind little monster made for the open side
of the nest, the only part where it could throw its
burden down the bank. [The latter remark has reference
to the position of the nest below a heather bush, on
the declivity of a low abrupt bank, where the only
chance of dislodging the young birds was to eject them
over the side of the nest remote from its support upon
the bank.] As the young cuckoo was blind, it must have
known the part of the nest to choose by feeling from
the inside that that part was unsupported.

Such being the facts, we have next to ask how they are to be explained on the principles of evolution. At first sight it seems that although the habit saves the bird which practises it much time and trouble, and so is clearly of benefit to the individual, it is not so clear how the instinct is of benefit to the species; for as cuckoos are not social birds, and therefore cannot in any way depend on mutual co-operation, it is difficult to see that this saving of time and trouble to the individual can be of any use to the species. But Jenner seems to have hit the right cause in the concluding part of the above quotation. If it is an advantage that the cuckoo should migrate early, it clearly becomes an advantage, in order to admit of this, that the habit should be formed of leaving her eggs for other birds to incubate. At any rate, we have here a sufficiently probable explanation of the _raison d'être_ of this curious instinct; and whether it is the true reason or the only reason, we are justified in setting down the instinct to the creating influence of natural selection.

Mr. Darwin, in his 'Origin of Species,' has some interesting remarks to make on this subject. First, he is informed by Dr. Merrell that the American cuckoo, although as a rule following the ordinary custom of birds in incubating her own eggs, nevertheless occasionally deposits them in the nests of other birds.

Now let us suppose that the ancient progenitor of our
European cuckoo had the habits of the American cuckoo,
and that she occasionally laid her egg in another
bird's nest. If the old bird profited by this
occasional habit through being able to migrate
earlier, or through any other cause; or if the young
were made more vigorous by advantage being taken of
the mistaken instinct of another species than when
reared by their own mother, encumbered as she could
hardly fail to be by having eggs and young at the same
time;[175] then the old birds or the fostered young
would gain an advantage.[176]

The instinct would seem to be a very old one, for there are two great changes of structure in the European cuckoo which are manifestly correlated with the instinct. Thus, the shape of the young bird's back has already been noted; and not less remarkable than this is the small size of the egg from which the young bird is hatched. For the egg of the cuckoo is not any larger than that of the skylark, although an adult cuckoo is four times the size of an adult skylark. And 'that the small size of the egg is a real case of adaptation (in order to deceive the small birds in whose nests it is laid), we may infer from the fact of the non-parasitic American cuckoo laying full-sized eggs.' Yet, although the instinct in question is doubtless of high antiquity, there have been occasional instances observed in cuckoos of reversion to the ancestral instinct of nidification; for, according to Adolf Müller, 'the cuckoo occasionally lays her eggs on the bare ground, sits on them, and feeds her young.'

In 'Nature' for November 18, 1869, Professor A. Newton, F.R.S., has published an article on a somewhat obscure point connected with the instincts of the cuckoo. He says that Dr. Baldamus has satisfied him, by an exhibition of sixteen specimens of cuckoos' eggs found in the nests of different species of birds, 'that the egg of the cuckoo is approximately coloured and marked like those of the bird in whose nest it is found,' for the purpose, no doubt, of deceiving the foster-parents. Professor Newton adds, however:--

Having said this much, and believing as I do the
Doctor to be partly justified in the carefully worded
enunciation of what he calls a 'law of nature,' I must
now declare that it is only 'approximately,' and by no
means _universally_ true that the cuckoo's egg is
coloured like those of the victims of her imposition,
&c.

Still, when so great an authority as Professor Newton expresses himself satisfied that there is a marked _tendency_ to such imitation, which in some cases leads to extraordinary variations in the colouring of the cuckoo's egg, the alleged fact becomes one which demands notice. The question, of course, immediately arises, How is it conceivable that the fact, if it is a fact, can be explained? We cannot imagine the cuckoo to be able consciously to colour her egg during its formation in order to imitate the eggs among which she is about to lay it; nor can we suppose that having laid an egg and observed its colouring, she then carries it to the nest of the bird whose eggs it most resembles. Professor Newton suggests another theory, which he seems to think sufficient, but which I confess seems to me little more satisfactory than the impossible theories just stated. He says:--

Only one explanation of the process can, to my mind,
be offered. Every person who has studied the habits of
birds with sufficient attention will be conversant
with the tendency which certain of those habits have
to become hereditary. It is, I am sure, no violent
hypothesis to suppose that there is a very reasonable
probability of each cuckoo most commonly placing her
eggs in the nest of the same bird, and of this habit
being transmitted to her posterity.

Now it will be seen that it requires but only an
application to this case of the principle of 'natural
selection,' or 'survival of the fittest,' to show that
if my argument be sound, nothing can be more likely
than that, in the course of time, that principle
should operate so as to produce the facts asserted,
the eggs which best imitated those of particular
foster-parents having the best chance of duping the
latter, and so of being hatched out.

Now, granting to this hypothesis the assumption that individual cuckoos have special predilections as to the species in whose nests they are to lay their eggs, and that some of these species require to be deceived by imitative colouring of the egg to prevent their tilting it out, there is still an enormous difficulty to be met. Supposing that one cuckoo out of a hundred happens to lay eggs sufficiently like those of the North African magpies (a species alluded to by Professor Newton) to deceive the latter into supposing the egg to be one of their own. This I cannot think is too small a proportion to assume, seeing that, _ex hypothesi_, the resemblance must be tolerably close, and that the egg of the magpie does not resemble the great majority of eggs of the cuckoo. Now, in order to sustain the theory, we must suppose that the particular cuckoo which happens to have the peculiarity of laying eggs so closely resembling those of the magpie, must also happen to have the peculiarity of desiring to lay its eggs in the nest of a magpie. The conjunction of these two peculiarities would, I should think, at a moderate estimate reduce the chances of an approximately coloured egg being laid in the appropriate nest to at least one thousand to one. But supposing the happy accident to have taken place, we have next to suppose that the peculiarity of laying these exceptionably coloured eggs is not only constant for the same individual cuckoo, but is inherited by innumerable generations of her progeny; and, what is much more difficult to grant, that the fancy for laying eggs in the nest of a magpie is similarly inherited. I think, therefore, notwithstanding Professor Newton's strong opinion upon the subject, that the ingenious hypothesis must be dismissed as too seriously encumbered by the difficulties which I have mentioned. We may with philosophical safety invoke the influence of natural selection to explain all cases of protective colouring when the _modus operandi_ need only be supposed simple and direct; but in a case such as this the number and complexity of the conditions that would require to meet in order to give natural selection the possibility of entrance, seem to me much too considerable to admit of our entertaining the possibility of its action--at all events in the way that Professor Newton suggests. Therefore, if the facts are facts, I cannot see how they are to be explained.

Cuckoos are not the only birds which manifest the parasitic habit of laying their eggs in other birds' nests.

Some species of _Melothrus_, a widely distinct genus
of American birds, allied to our starlings, have
parasitic habits like those of the cuckoo; and the
species present an interesting gradation in the
perfection of their instincts. The sexes of _Melothrus
cadius_ are stated by an excellent observer, Mr.
Hudson, sometimes to live promiscuously together in
flocks and sometimes to pair. They either build a nest
of their own, or seize on one belonging to some other
bird, occasionally throwing out the nestlings of the
stranger. They either lay their eggs in the nest thus
appropriated, or oddly enough build one for themselves
on the top of it. They usually sit on their own eggs
and rear their own young; but Mr. Hudson says it is
probable that they are occasionally parasitic, for he
has seen the young of this species feeding old birds
of a distinct kind and clamouring to be fed by them.
The parasitic habits of another species of
_Melothrus_, the _M. Canariensis_, are much more
highly developed than those of the last, but are still
far from perfect. This bird, as far as it is known,
invariably lays its eggs in the nests of strangers,
but it is remarkable that several together sometimes
commence to build an irregular untidy nest of their
own, placed in singularly ill-adapted situations, as
on the leaves of a large thistle. They must, however,
as far as Mr. Hudson has ascertained, complete a nest
for themselves. They often lay so many eggs, from
fifteen to twenty, in the same foster-nest, that few
or none can possibly be hatched. They have, moreover,
the extraordinary habit of pecking holes in the eggs,
whether of their own species or of their
foster-parents, which they find in the appropriated
nests. They drop also many eggs on the bare ground,
which are thus wasted. A third species, the _M.
precius_ of North America, has acquired instincts as
perfect as those of the cuckoo, for it never lays more
than an egg in a foster-nest, so that the young bird
is securely reared. Mr. Hudson is a strong disbeliever
in evolution, but he appears to have been so much
struck by the imperfect instincts of the _Melothrus
Canariensis_ that he quotes my words, and asks, 'Must
we consider these habits not as especially endowed or
created instincts, but as small consequences of one
general law, namely transition?'[177]

Such are all the facts and considerations which I have to present with reference to the curious instinct in question. It will be seen that--with one doubtful or not sufficiently investigated exception, viz., that of cuckoos adapting the colour of their eggs to that of the eggs of the foster-parents--there is nothing connected with these instincts that presents any difficulty to the theory of evolution. We may, perhaps, at first sight wonder why some counteracting instinct should not have been developed by the same agency in the birds which are liable to be thus duped; but here we must remember that the deposition of a parasitic egg is, comparatively speaking, an exceedingly rare event, and therefore not one that is likely to lead to the development of a special instinct to meet it.

_General Intelligence._

Under this heading I shall here, as in the case of this heading elsewhere, string together all the instances which I have met with, and which I deem trustworthy, of the display of unusually high intelligence in the class, family, order, or species of animals under consideration--the object of this heading in all cases being that of supplying, by the facts mentioned beneath it, a general idea of the upper limit of intelligence which is distinctive of each group of animals.

That birds recognise their own images in mirrors as birds there can be no question. Houzeau, who records observations of his own in this connection with parrots,[178] adds that dogs are more difficult to deceive by mirrors in this way than birds, on account of their depending so much upon smell for their information. No doubt individual differences are to be met with in animals of both classes, and much depends on previous experience. Young dogs, or dogs which have never seen a mirror before, are not, as a rule, difficult to deceive, even though they have good noses. I myself had a setter with an excellent nose, who on many repeated occasions tried to fight his own image, till he found by experience that it was of no use. As to birds, I have seen canaries suppose their own images to be other canary birds, and also the reflection of a room to be another room--the birds flying against a large mirror and falling half stunned. I mention the latter circumstance because it afforded evidence of the superior intelligence of a linnet, which on the same occasion dashed itself against the mirror once, but never a second time, while the canaries did so repeatedly.

Mrs. Frankland, in 'Nature' (xxi., p. 82), gives the following account of a bullfinch paying more attention to a portrait of a bullfinch than to his own image in a mirror, which is certainly remarkable; and as the fact seems to have been observed repeatedly, it can scarcely be discredited:

The following is a curious instance of discrimination
which I have observed in my bullfinch. He is in the
habit of coming out of his cage in my room in the
morning. In this room there is a mirror with a marble
slab before it, and also a very cleverly executed
water-colour drawing of a hen bullfinch, life size.
The first thing that my bullfinch does on leaving his
cage is to fly to the picture (perching on a vase just
below it) and pipe his tune in the most insinuating
manner, accompanied with much bowing to the portrait
of the hen bullfinch. After having duly paid his
addresses to it, he generally spends some time on the
marble slab in front of the looking-glass, but without
showing the slightest emotion at the sight of his own
reflection, or courting it with a song. Whether this
perfect coolness is due to the fact of the reflection
being that of a cock bird, or whether (since he shows
no desire to fight the reflected image) he is
perfectly well aware that he only sees himself, it is
difficult to say.

That birds possess considerable powers of imagination, or forming mental pictures of absent objects, may be inferred from the fact of their pining for absent mates, parrots calling for absent friends, &c. The same fact is further proved by birds dreaming, a faculty which has been noticed by Cuvier, Jerdon, Thompson, Bennet, Houzeau, Bechstein, Lindsay, and Darwin.[179]

The facility with which birds lend themselves to the education of the show-man is certain evidence of considerable docility, or the power of forming novel associations of ideas. Thus, according to Bingley,--

Some years ago the Sieur Roman exhibited in this
country the wonderful performances of his birds. These
were goldfinches, linnets, and canary birds. One
appeared dead, and was held up by the tail or claw
without exhibiting any signs of life. A second stood
on its head, with its claws in the air, &c., &c.[180]