As it is impossible to detail in one brief essay all the species of fly-catcher found in the Indian hills, I propose merely to mention those that are most common in the Nilgiris and the Himalayas, and then to make a few observations on fly-catchers in general. In addition to the fan-tail, the grey-headed and the brown fly-catchers, the following species are abundant in the Nilgiris: Tickell’s blue fly-catcher (Cyornis tickelli), the Nilgiri blue fly-catcher (Stoparola albicaudata), and the black and orange fly-catcher (Ochromela nigrirufa). In the Himalayas, the paradise fly-catcher is common in summer at lower altitudes. Above 6000 feet elevation the following are the species most commonly seen: the grey-headed fly-catcher, the white-browed blue fly-catcher (Cyornis superciliaris), and the beautiful verditer fly-catcher (Stoparola melanops), which is no mean songster.
Fly-catchers form a most interesting group of birds. It is, I maintain, quite impossible for any man possessed of a logical mind to contemplate this family without discovering that the theory of natural selection is utterly inadequate to account for the variety of animal life that exists upon the earth. The habits of practically all the fly-catchers are identical. They all dwell in an arboreal habitat; nevertheless, the various species display great dissimilarity in outward appearance. Some species are brightly plumaged, others are as dully clad as a bird can possibly be. Some have crests and long tails, others lack these ornaments. The adult cock paradise fly-catcher, with his long, white, satin-like tail feathers, is the most striking of birds, while the brown fly-catcher is less conspicuously attired than a hen sparrow. This is not the only difficulty presented to the theory of natural selection by fly-catchers. In some species, as, for example, the paradise fly-catcher, the sexes are altogether dissimilar in appearance, while in others the most practised eye cannot distinguish between the cock and the hen. Nor does there appear to be any connection between nesting habits and the presence or absence of sexual dimorphism. The fan-tail fly-catchers, in which the sexes are alike, and the paradise fly-catchers, in which they differ widely, both build little cup-shaped nests in the lower branches of trees, and in both the cock shares with the hen the duty of incubation. Again, the verditer and the white-browed blue fly-catchers build their nests in holes in trees; yet in the former both sexes are blue, while in the latter the cock only is blue.
Further, in the fly-catchers we see every gradation of sexual dimorphism, from a difference so slight as to be perceptible only when the sexes are seen side by side, to a difference so great as to make it difficult to believe that the sexes belong to one and the same species. It must, therefore, be obvious to any sane person that neither natural nor sexual selection can be directly responsible for the colouration of many species of fly-catcher.
Another interesting characteristic of the fly-catchers is the total absence of green in the plumage of any of them. They are birds of a variety of colours; they display many shades of blue, yellow, orange, red, grey, and brown, also black and white; but not one carries any green feathers. Yet they are essentially arboreal birds, so that green would be a very useful colour to them from the point of view of protection from enemies. From the fact, then, that none of the fly-catchers are green, we seem to be compelled to infer that there is something in their constitution that prevents green variations appearing in their plumage.
In conclusion, note must be made of the fact that fly-catchers, although they subsist almost entirely upon insect diet, appear but rarely to devour butterflies. I have watched fly-catchers closely for several years, and have on two occasions only seen them chase butterflies or moths. Five years ago in Madras I observed a paradise fly-catcher chasing a small butterfly, and recently, in the Himalayas, I saw a grey-headed fly-catcher drop down from a tree and seize a moth that was resting in the gutter. The reason why fly-catchers do not often attack butterflies is obvious; these insects offer very little meat and a great deal of indigestible wing surface. Nevertheless, the theory of protective mimicry is almost exclusively illustrated by examples taken from butterflies. In theory, these creatures are so relentlessly persecuted by insectivorous birds that in order to escape their foes many edible butterflies mimic the appearance of unpalatable species. Unfortunately for theory, few creatures in practice seem to attack butterflies when on the wing, which is just the time when the “mimicry” is most obvious.
The elegant little fly-catchers, then, are birds which mock Darwin, laugh at Wallace, and make merry at the expense of Muller and Bates!
XXXIII
INSECT HUNTERS
Fly-Catchers, although they subsist almost entirely on insects, are by no means the only insectivorous creatures in existence. They merely form a considerable branch of the Noble Society of Insect Hunters.
If there exist any philosophers in the insect world they must find the uncertainty of life a fitting theme on which to lavish their philosophical rhetoric. Consider for a moment the precariousness of the life of an insect! There exist in India probably over three hundred species of birds which live almost exclusively upon an insect diet. Think of the mortality among insects caused by these birds alone, by the mynas, the swifts, the bee-eaters, the king crows, et hoc genus omne. Then there are insectivorous mammals, to say nothing of man who yearly destroys millions of injurious and parasitic hexapods. Fish too are very partial to insects, while for spiders, frogs, and lizards, life without insects would be impossible. Nor do the troubles of insects end here, they are preyed upon by their own kind, and, strange phenomenon, some plants entrap and destroy them. But we Anglo-Indians cannot afford to sympathise with the insects. In spite of the high mortality of the hexapod tribes, they flourish like the green bay-tree. So prolific are they that, notwithstanding the fact that millions are daily destroyed by their foes, the life of human beings in India becomes a burden on account of the creeping things. In the monsoon the insects tax man almost to the limits of his endurance—they teaze, bite, and worry his person, they destroy his worldly goods, and, not content with this, find their way into his food and drink. For this reason I feel very kindly disposed to the frogs, the lizards, and the fly-catching birds.
It is worth coming to India if only to see a frog or toad at work. Go at sunset, during a break in the rains, on to the chabutra, and place a lamp near you. Thousands of insects of all shapes and sizes are attracted by the light. In their wake come the toads. A toad always looks blasé. His stupid appearance and sluggish movements give him this air. Watch him as he hops into the zone of light. He advances to within an inch of a resting insect, and, before you can say “Jack Robinson,” the creature has flown into his mouth! The toad takes another hop, and a second insect follows the example of the first; then another and another! Have the insects all suddenly gone mad? Are they bewitched, mesmerised by the ugly face of the toad? Nothing of the kind. The insects have not jumped into the amphibian’s mouth at all. The toad has a long tongue attached at the front end to its mouth. This tongue is covered with sticky saliva and is capable of being protruded and retracted with lightning rapidity. In other words, the toad’s tongue is just a fly-paper, capable of the most perfect manipulation. The unsuspecting insect is resting, and hears not the silent approach of its enemy. Suddenly it is caught up by a great sticky tentacle, then comes oblivion. The toad’s tongue has shot forth and back again so quickly as to be imperceptible to the human eye.