Birds of the Plains

by Douglas Dewar

Want of space prevents further dilation upon this fascinating subject.

To sum up the conclusions I desire to emphasise. A bird has during the greater part of its life only to look after itself, and the more intelligent it be the better will it do this, hence natural selection tends to increase the intelligence of birds. But, at certain seasons, it becomes all-important to the species that the adults should attend to their young, even at risk to themselves. To secure this Nature has placed inside birds a force, dormant at most times, which at periodic intervals completely overrides all normal instincts, a force which compels parent birds to rivet their attention on the nest and its contents. Thus the sudden conversion of birds into automata is a necessity, not a mere whim of Dame Nature. The instinct is not of very long duration; for as soon as the young are able to fend for themselves, the parents sometimes behave in what seems to human beings a most unnatural way: they drive off their offspring by force. As a matter of fact, this behaviour is quite natural; it is dictated by Nature for the benefit of the species. Strong as the maternal instinct is, it is liable to be overridden by stronger instincts, such as that of migration. When the time for the migratory journey comes round, the parent birds will desert, without apparently a pang of remorse, or even a thought, the broods for whose welfare they have been slaving day and night. This desertion of later broods by migratory birds is far commoner than is generally supposed. In 1826 Mr. Blackwell inspected the house-martins’ nests under the eaves of a barn at Blakely after the autumnal migration of these birds. Of the twenty-two nests under the eaves inspected on 11th November, no fewer than thirteen were found to contain eggs and dead nestlings.

PLAYING CUCKOO

Ornithological experience led me some time back to the belief that at the nesting season a bird becomes a creature of instinct, an organism whose actions are, for the time being, those of a machine, a mere automaton. This view, which has been set forth in the preceding article, is not held by all naturalists. I therefore determined to undertake a systematic series of experiments with a view to putting it to the test. In other words, I decided to play cuckoo. I selected the Indian crow (Corvus splendens) as the subject of my experiments, because it is the most intelligent of the feathered folk. If it can be proved that when on the nest the actions of this bird are mechanical, it will follow that the less intelligent birds are likewise mere automata when incubating. Another reason for selecting the crow as my victim is that I have been investigating the habits of the koel (Eudynamis honorata), which is parasitic on the crow, and in so doing have had to visit a large number of crows’ nests.

The crow lays a pale blue egg blotched with brown, while the egg of the koel is a dull olive-green also blotched with brown. It is considerably smaller than the crow’s egg. I have seen dozens of koel’s eggs, but never one that a human being could possibly mistake for that of a crow, yet our friend Corvus is unable to detect the strange egg when deposited in the nest and sits upon it. It is not that birds are colour-blind. The koel is able to distinguish its own egg from that of the crow, for, after it has deposited its egg, it frequently returns to the nest and removes one or more of the crow’s eggs! I am convinced that ordinarily a crow would have no difficulty in distinguishing between the two kinds of egg; but at the nesting time it throws most of its intelligence to the winds and becomes a puppet in the hands of its instincts, which are to sit upon everything in the nest.

I have myself placed koel’s eggs in crows’ nests, and in every case the crow has incubated the eggs. On one occasion I came upon a crow’s nest containing only two koel’s eggs. As the nest was some way from my bungalow and in an exposed situation, I knew that, the moment I left, it would be robbed by some mischievous native boy, so I took the eggs and placed them in a crow’s nest in my compound. This already contained three crow’s eggs, two of which I moved, substituting the koel’s eggs for them. The crow’s eggs had only been laid three or four days, but the koel’s eggs were nearly incubated, since both yielded chicks on the third day after I placed them in the nest. If nesting crows think, that pair must have been somewhat surprised at the speedy appearance of the chicks!

In all, I have placed six koel’s eggs in four different crow’s nests, and as I have already said, in no single instance did the trick appear to be detected. In the majority of cases, I did not trouble to keep the number of eggs in the nest constant. I merely added the koel’s egg to those already in the nest.

But I have put my theory to a much more severe test. In a certain crow’s nest containing two eggs I put a large fowl’s egg. This was cream-coloured and fully three times the size of the crow’s egg, yet within ten minutes the crow was sitting comfortably on the strange egg. She did not appear to notice the considerable addition to her clutch. She subsequently laid three more eggs, so that she had six eggs to sit upon, five of her own and the large fowl’s egg! Day after day I visited the nest and watched the progress of the strange egg. On the twentieth day the chick inside was moving, but when I went to the nest on the twenty-first day I discovered that some one had climbed the tree, for several branches were broken. Two young crows had been taken away and the fowl’s egg thrown upon the ground. There it lay with a fully formed black chicken inside! I have that chicken in a bottle of spirit. Subsequent inquiry showed that the dhobi’s son had taken it upon himself to spoil my experiment. However, it went sufficiently far to prove that crows may one day become birds of economic value; why not employ them as incubators? Had the crow come across that chick’s egg anywhere but in its nest, it would undoubtedly have made its breakfast off it.

I repeated the experiment in another nest. This time the chick hatched out. When it appeared the rage of the crows knew no bounds. With angry squawks the scandalised birds attacked the unfortunate chick, and so viciously did they peck at it that it was in a dying state by the time my climber reached the nest.

With a view to determining at what stage the incubating instinct secures its dominance, I placed another fowl’s egg in a crow’s nest that was almost ready to receive eggs, wondering whether the presence of this egg would stimulate the crow to lay, without troubling to give the final touches to the nest. The bird devoured the egg. It is my belief that the acts of a nesting bird do not become completely automatic until it has laid an egg in the nest. If one visits a crow’s nest which is in course of construction, the owners will as likely as not desert it; but I have never known a crow desert its nest when once it has laid an egg—provided, of course, he who visits the nest leaves any eggs in it.