The Indian grosbeaks are birds of limited distribution; they appear to be confined to the forests on the higher ranges of the Himalayas. Their most striking feature is the stout conical bill, which is an exaggeration of that of the typical finch, and is responsible for the bird's name. In one genus of grosbeak--Mycerobas--the bill is as deep as it is long, while in the other genus--Pycnorhamphus--it is nearly as massive. Three species belonging to this latter genus occur in India, namely, P. icteroides, the black-and-yellow grosbeak, found in the Western Himalayas; P. affinis, the allied grosbeak, found in Nepal, Sikkim, Tibet, and Western China; and P. carneipes, the white-winged grosbeak, which occurs all along the higher Himalayas.
There is only one Indian species of the other genus; this is known as the spotted-winged grosbeak (Mycerobas melanoxanthus), the localities in which this occurs are said to be "the Himalayas from the Hazara country to Sikkim at considerable elevations and Manipur."
The only Indian grosbeak which I have met in the flesh is the yellow-and-black species. This bird is common in the hills round about Murree, so that, when on ten days' leave there, I had some opportunity of studying its habits. It is a bird of the same size as the Indian oriole (Oriolus kundoo). The cock grosbeak, indeed, bears a striking resemblance to the black-headed oriole (Oriolus melanocephalus). His whole head, chin, throat, wings, shoulders, upper-tail-coverts, and thighs are black, the remainder of the plumage is a rich yellow, tinged with orange at the hind neck. Thus the colour and markings are almost identical with those of the black-headed oriole, the chief difference being that the latter has a little yellow in the wing. So great is the resemblance that the casual observer will, in nine cases out of ten, mistake the grosbeak for an oriole. The resemblance extends to size and shape, as the following table shows:
Length Length Length Length Length
of Bird. of Tail. of Wing. of Tarsus. of Beak.
Grosbeak . . 9.0 in. 3.7 in. 5.2 in. 1.0 in. 1.0 in.
Oriole . . . 9.5 " 3.4 " 5.4 " 1.0 " 1.3 "
Length Length Length Length Length of Bird. of Tail. of Wing. of Tarsus. of Beak. Grosbeak . . 9.0 in. 3.7 in. 5.2 in. 1.0 in. 1.0 in. Oriole . . . 9.5 " 3.4 " 5.4 " 1.0 " 1.3 "
The hen grosbeak differs considerably in colour and marking both from the cock of her species and from the hen black-headed oriole. She is a dull ashy-grey bird, tinged faintly with yellowish red on the back and abdomen. Her wings and tail are black. The only young grosbeak that I have seen resembled the female in appearance, except that it had a yellow rump. It was being fed by a cock bird.
Grosbeaks live in forests, and go about either in couples or in small companies. They seem to feed largely on the ground, picking up insects. The beak of the finch tribe is adapted to a diet of seeds; nevertheless, many finches vary this food with insects. I saw a grosbeak seize, shake, and devour a caterpillar about two inches in length. Grosbeaks also eat berries and stone fruit. When disturbed they at once betake themselves to a tree, among the branches of which they are able to make their way with great agility. Grosbeaks are restless birds, always on the move, here to-day and gone to-morrow. The cock emits a call at frequent intervals. This is not easy to describe. It sounds something like kiu kree.
The nest is a cup-shaped structure, composed exteriorly of twigs, grass, and moss, and lined with stalks of maiden-hair fern and fine roots. It is usually placed high up in a fir tree. Colonel Rattray believes that the birds bring up two broods in the year. They lay first in May, and, as soon as the young are able to shift for themselves, a second nest is made. Thus in July both young birds at large and nests with eggs are likely to be seen. The eggs are not unlike those of the English hawfinch; the ground colour is pale greenish grey, blotched and spotted with blackish brown. Sometimes the markings occur chiefly at the broad end of the eggs.
The most striking feature of the black-and-yellow grosbeak, and that on which I wish particularly to dwell, is the extraordinary resemblance that the cock bird bears to the cock black-headed oriole. If this extended to the hen, and if the grosbeak were parasitic on the oriole, it would be held up as an example of mimicry. We should be told that owing to its resemblance to its dupe it was able to approach the nest without raising any suspicion and deposit its egg. But the grosbeak is not parasitic on the oriole, and it is the cock and not the hen that bears the resemblance; moreover, the black-headed oriole does not occur in the Himalayas, so that neither the grosbeak nor the oriole can possibly derive any benefit from this resemblance.
Now, cabinet zoologists are never tired of writing about mimicry. They assert that when organisms belonging to different families bear a close external resemblance, this resemblance has been brought about by natural selection. Having made this assertion, they expend reams of paper in demonstrating how one or both of the species benefits by the resemblance.
However, scientific books make no mention of the resemblance between the oriole and the grosbeak. The reason for this is, of course, that the resemblance in this instance cannot be a case of mimicry. Now, I regret to have to say that men of science take up the same attitude towards their theories as lawyers do regarding the cases they argue in Courts of Justice. There would be no harm in taking up this attitude if men of science were to explain that they are acting the part of advocates, that they are fighting for a theory, and trying to persuade the world to accept this theory. It is because they masquerade as judges, and put forward a one-sided case as a matured judicial finding, that I take exception to their methods.
The trouble is that scientific men to-day form a brotherhood, a hierarchy, which lays claim to infallibility, or rather tacitly assumes infallibility.
They form a league into which none are admitted except those who take the oath of allegiance; and, of course, to expose the weakness of the scientific doctrines of the time is equivalent to violating the oath of allegiance. Now, the man of science who has to earn his living by his science, has either to join the league or run the risk of starving. This explains how a small coterie of men has things very much its own way; how it can lay down the law without fear of contradiction. If a man does arise and declines to accept the fiats of this league, it is not difficult for the members to combine and tell the general public that that man is a foolish crank, who does not know what he is talking about; and the public naturally accepts this dictum.
The only scientific men who, as a class, are characterised by humility are the meteorologists. I always feel sorry for the meteorologist. He has to predict the weather, and every man is able to test the value of these predictions. The zoologist, on the other hand, does not predict anything. He merely lays down the law to people who know nothing of law. He assures the world that he can explain all organic phenomena, and the world believes him.
As a matter of fact, zoology is quite as backward as meteorology. Those who do not wish to be deceived will do well to receive with caution all the zoological theories which at present hold the field. Before many years have passed all of them will have been modified beyond recognition. Most of them are already out of date.
There are doubtless good reasons for the colouring of both the grosbeak and the oriole; what these reasons are we know not. But as neither derives any benefit from the resemblance to the other, this resemblance cannot have been effected by natural selection. Now, if the unknown forces, which cause the various organisms to take their varied colours and forms, sometimes produce two organisms of different families which closely resemble one another, and the organisms in question are so distributed that neither can derive the slightest advantage in the struggle for existence from the resemblance, there is no reason why similar resemblances should not be produced in the case of organisms which occupy the same areas of the earth. Thus it is quite possible that many so-called cases of mimicry are nothing of the kind.
The mere fact that one of the organisms in question may profit by the likeness is not sufficient to demonstrate that natural selection is responsible for the resemblance.
In this connection we must bear in mind that, according to the orthodox Darwinian theory, the resemblance must have come about gradually, and in its beginnings it cannot have profited the mimic as a resemblance.
So plastic are organisms, and so great is the number of living things in the earth, that it is not surprising that very similar forms should sometimes arise independently and in different parts of the globe. Several instances of this fortuitous resemblance are cited in Beddard's Animal Colouration; others are cited in The Making of Species by Finn, and myself.
Perhaps the most striking case is that of a cuckoo found in New Zealand, known as Eudynamis taitensis. This is a near relative of the Indian koel, which bears remarkable resemblance to an American hawk (Accipiter cooperi). Writing of this cuckoo, Sir Walter Buller says: "Not only has our cuckoo the general contour of Cooper's sparrow-hawk, but the tear-shaped markings on the underparts, and the arrow-head bars on the femoral plumes are exactly similar in both. The resemblance is carried still further, in the beautifully-banded tail and marginal wing coverts, and likewise in the distribution of colours and markings on the sides of the neck. On turning to Mr. Sharpe's description of the young male of this species in his catalogue of the Accipitres in the British Museum, it will be seen how many of the terms employed apply equally to our Eudynamis, even to the general words, 'deep brown above with a chocolate gloss, all the feathers of the upper surface broadly edged with rufous.' ... Beyond the general grouping of the colours there is nothing to remind us of our own Bush-hawk; and that there is no great protective resemblance is sufficiently manifested, from the fact that our cuckoo is persecuted on every possible occasion by the tits, which are timorous enough in the presence of a hawk."
These cases of chance resemblance should make us unwilling to talk about "mimicry," unless there is actual proof that one or other of the similar species benefits by the resemblance.
These cases, further, throw light on the origin of protective mimicry where it does exist.
Protective mimicry is usually said to have been brought about by the action of natural selection. This is not strictly accurate. Natural selection cannot cause two showy, dissimilar species to resemble one another; all it can do is to seize upon and perfect a resemblance that has been caused by the numerous factors that have co-operated to bring about all the diversity of organic life upon this earth.