WCP5133

[1]¹ [p. 390]

The following extracts from a letter just received from Mr. R. R. Mortimer, of Hanover Road, Cape Colony, contain some observations which will, I think, be of interest to naturalists, and therefore worth recording in the pages of Nature.

Alfred R. Wallace.

"Since reading 'Darwinism,' powers of observation have unconsciously been gained by me. Day by day nature has some phenomena quite new to me, which phenomena would probably never have been observed by me if I had not had the good fortune to have digested the principles if the Darwinian Theory so obviously explained by you. From the time of reading the book till now I have observed peculiarities of organic beings in this part of the world. These observances I relate: (1) The first observation I particularly remember was in regard to a peculiar action of a small bird, indefinitely termed by Colonials, snipe. What their specific or proper name is I cannot say since the title of naturalist is not claimed by me. These snipe in question, or individuals of the variety, made their nests on mounds of dung which were practically the accumulated refuse of old sheep kraals. The shape of the nest was simply a hole scooped out on top of a mound. The colour of the refuse was a variegated dark brown and black. The eggs of such birds fully corresponded in colouration with the environment or surroundings. As a means of concealment, the colouration of the eggs was perfect. It required an extreme amount of careful inspection to and search to detect the eggs in a nest on such mounds. When you came across the nest, you would find it was perfectly open and uncovered by any material; therefore you would presume the owners of the nest distinctly relied upon the colouration of their eggs to defy detection. But if by chance you detected a nest, and the owners were present, by holding yourself perfectly immovable and stationary, one bird would immediately approach its nest, and gradually cover it by scooping dust over the eggs with the action of its feet.

This recourse to hiding its nest from view is only adopted on extreme occasions, when their sense-action gives them the knowledge that the enemy present has perceived its contents, or the nest itself.

There must be double selective agency in this mode of concealment at work.

As far as my knowledge goes, our so defined snipe generally frequent localities where water is present. Now the same variety in question do make their habitat on banks of rivers, or where water is to be found; yet here I have noticed individuals of the same variety diverge from the specific character, take up a new area, if even only temporarily, where their eggs can be laid with more safety. It is an indisputable fact that the colouration of the snipe eggs is in union and harmony with the environment as a means of protection, yet here we find individuals of the same variety possessing the last possible resort of concealing its eggs— namely, covering them over with a material so as to defy any minute detective powers.

Surely the struggle for existence must, in this case, be extremely severe, and the principle of natural selection in full activity.

(2) Having had practical experience in farming with ostriches, and their domestication, I may say a few words on them.

Ostriches have, so to say, no means of indirectly concealing their eggs; but the only means of concealing their nest is by their personal presence. The hen does her share of sitting in the daytime, her drab-coloured plumage being in harmony with the surroundings. The cock replaces her on the nest at evening time, sitting throughout the night, and generally on to 8 a.m., his black plumage corresponding with the shades of night; therefore you have some difficulty, sometimes very great, in detecting the nest of an ostrich.

In addition to this remarkable adaptation of sexual colouration, the cock takes the role of a guard patrolling up and down some distance off the nest. When he perceives that mischief is bent upon the eggs by the approach of a person, he almost invariably charges him, and, woe betide if the person is destitute of some means of defence. To deliberately go up to a nest in the presence of its lord without some weapon or means of protection is considered by Colonials to be the height of foolishness and ignorance.

But invariably again, on the other hand, when you have succeeded so far in reaching the nest, and handling its eggs, the cock quiets down.

He loses all his viciousness, falls down alongside the nest, gives vent to, apparently, appeals for mercy, by continuously flapping his wings against the ground and giving forth sounds by means of his beak, of a peculiar dull clicking character.

Domestication has made ostriches feel less fear for human beings, at the same time giving a more vigorous character to their viciousness.

Some two years ago, among a troop of ostriches that were bought down to the farm where I was gaining my experience, there was one ostrich, a male bird in every respect in its external character and colouration of plumage. It was to all possible appearance a cock, and yet it had been seen on two occasions [2] [p. 391] to be paired by a true cock ostrich. This particular ostrich was a hen, although she had every appearance of being a cock. What explanation could you give as regards this incongruity?

(3) About six months ago I found a peculiar bird’s nest suspended from the root of a mimosa tree which overlapped a bank of ground. Before going further, I must tell you that previous to the occasion in question I noticed them same peculiar form of nest, but it seemed so utterly impossible at the time that it could be a nest, since its structure and mode of suspension had the exact characteristics of a certain structural spider’s web, that I passed it by. But on the second occasion to make absolutely sure that I had not made a mistake, I went up and cut the nest off, with a certain length of the root to which it was attached. Imagine my surprise, when I saw that it was really a bird’s nest with two eggs. Now this nest was a perfect facsimile of a common spider’s web and home, found in the locality where I was at the time of staying.

Since it was a marvellous imitation of an insect’s habitat, there must have must have been some corresponding necessity for such imitation. Either the nest must have been designed and constructed, so as to delude enemies by which the species was liable to be attacked, or, it was so imitated, that the materials of which the nest was made should serve as bait, and allow the parent birds to be able to feed their young without the necessity of having to leave the nest, and so be unable to protect their young for the time being. The materials from which the nest was made were practically webs abandoned by their original owners. It was an instance of perfect imitation."