Green pigeons are said to be far less obtrusive in their courtship than the majority of their kind. The male does not puff himself out after the manner of other cock pigeons, but is content to bow before his lady love and in this attitude move his expanded tail up and down.
There are few birds that assimilate so closely to their surroundings as green pigeons. Fifty of them may be perched in a pipal tree, and a man on the look-out for them may fail to detect a single individual until one of the birds moves. They are thus excellent examples of protectively coloured birds. Their green livery undoubtedly affords them a certain amount of protection, and so may perhaps be considered a product of natural selection. Be this as it may, a consideration of the details of the colouring of their plumage shows that many of these, as, for example, the lilac on the wing, are quite unnecessary for the concealment of the bird. The eastern and the southern species which occur together in certain places and the hybrids produced by the interbreeding of these are all equally difficult to distinguish from the surrounding leaves, notwithstanding the fact that their plumage differs in details, e.g. the breast and the abdomen are greenish yellow in the southern and ashy-grey in the eastern form, while there is green in the forehead and tail of the latter, but not of the former. Thus we have two species of green pigeon, of which at least one has not originated by natural selection. Facts such as these, however, do not prevent Dr. Wallace, Sir E. Ray Lankester, and Professor Poulton continually proclaiming from the housetops that every existing species owes its origin to natural selection and nothing but natural selection!
There are several genera of green pigeons, and all of them are characterised by short legs and broad toes. These are adaptations to the arboreal habit, in the formation of which natural selection has, in all probability, played an important part. The habits of all the genera are identical. They, one and all, build the rough-and-ready shakedowns which do duty for nests amongst the Columbidæ. All lay the inevitable two white eggs. Yet the sexes of the genus Crocopus are alike in external appearance, while those of the genera Osmosteros, Sphenocercus, and Treron exhibit considerable dimorphism. Again in the genus Butreron the sexual differences displayed are inconsiderable. These facts, of themselves, are quite sufficient to disprove the theory that sexual dimorphism in birds is due to the hen’s greater need of protection. Cock green pigeons assimilate so well to their leafy environment that there cannot possibly be any necessity for their wives to be differently dressed. Further, it is worthy of note that the most flourishing of the genera of green pigeons is that in which the sexes dress alike.
XXIII
BULBULS’ NESTS—I
In May, 1911, a pair of red-whiskered bulbuls (Otocompsa emeria) took up their residence in my verandah at Fyzabad, that is to say, they spent the greater part of the day there in constructing a nest in a croton plant. The nest of the bulbul is a shallow cup, formed of bast, roots, twigs, and grass, loosely worked together. Sometimes dead leaves, pieces of rag and other oddments are woven into the fabric of the nest. The pair of bulbuls of which I write did not, however, indulge in any of these luxuries; they were content with a rudely constructed nursery. When the nest was nearly complete the owners deserted it. Why they acted thus I have not been able to discover.
The bulbuls absented themselves for a few days. When they returned they frequented another portion of the verandah, and their fussiness betrayed the fact that they were working at another nest. Several days passed before I found time to look for their nest, and I then discovered it in an aralia plant growing in the verandah, in a large pot placed at the right-hand side of one of the doors leading into my office room. The site chosen was the more remarkable in that it was within ten feet of the carpet on which the chaprassis sit when not engaged in active work. This nest was of even rougher design than the first one, and was equally devoid of decoration. So carelessly had it been constructed that, to use a nautical expression, it had a distinct list. I found in the nest three pinkish eggs, mottled and blotched with purplish red. They had been laid some time before I first saw them. This was demonstrated by the reluctance of the hen to leave the nest when I approached. Among birds the parental instinct increases as incubation proceeds. On one occasion the bird sitting on the nest in question allowed me to stroke its tail. This organ projects upwards like a semaphore, the nest not being sufficiently large to accommodate it.
It was not until the 15th July that I had leisure to watch these bulbuls closely. Up to that time I had merely noticed that both birds incubate, and that both sexes, and not the cock alone, as some writers assert, have the red “whiskers,” or feathers, on the cheeks.
The weather being warm, it was not necessary for the birds to sit continuously, and the eggs were frequently left for ten minutes or longer at a time. On the morning of the 15th July, I found that two of the young birds had hatched out. Both parents were feeding them.
Birds are creatures of habit. Each parent bulbul had its own way of approaching the nest and of perching when tending the nestlings, so that, although I was not able to say for certain which of the pair was the cock and which the hen, I could distinguish one individual from the other. For brevity I will call them A and B, respectively.
Both birds, before flying to the nest, used to alight on the stem of a palm standing in the verandah. From this point their manœuvres differed. Individual A invariably flew to a stout vertical branch of the aralia, remained there for a second or two, flitted to a second vertical branch, and from thence hopped on to the edge of the nest, so that its face when there pointed to the east. This individual always showed itself the bolder spirit of the two. The other bird, B, used to fly from the palm to a slender leafy branch of the aralia, and thus cause considerable commotion among the leaves; from thence it jumped on to the edge of the nest, where it perched with its face pointing to the north. The modus operandi of A was the superior. The verandah faces the east, so that when A wished to leave the nest, it had but to jump across it into the space beyond, and then wing its way ahead, while B had to turn round before it could fly off. The neatness and address with which A used to leap across the nest into the air baffles description.