Page:The Zoologist, 4th series, vol 3 (1899).djvu/200

174 for the eggs to be unnoticeable from below, the natural course for the birds to take would be to build solid-bottomed nests always. Nor has it yet been proved that a white egg is less conspicuous from below than a coloured one. Mr. Beddard has shown that white is not invisible from below,—that a snowflake, when seen against a blue sky, looks black. If the colours of eggs have any meaning, they are obviously a protection against marauders above the nest. It is not usual for eggs laid in open nests to be white, even when dense foliage overhangs them. The eggs being white and the nest so flimsy, it might be supposed that until recently these birds built in holes. But the fact that by far the majority of the members of this great family (Columbidæ)—which embraces some three hundred species—does not nest in holes is a very strong argument against such a theory. These birds lay but two eggs, and often begin to sit as soon as the first egg is laid. In this way the need of colour would to some extent be obviated.

(c) Lastly, we must turn our attention to the Alcidæ. The eggs of the Common Guillemot display an extraordinary variety in ground colour and markings. Dr. Wallace and Mr. Dixon suppose that this is due to their being laid on inaccessible cliffs, and thus completely protected from enemies. If this is the correct explanation, it seems strange that the eggs should be coloured at all. But a visit to Flamborough Head in the breeding season will show that these eggs are not safe from all marauders. These cliffs are tenanted by Jackdaws as well as by Guillemots. And that the former have a taste for the eggs of the latter is evident, for the shells of sucked eggs may be seen lying about on the top of the cliffs. Prof. Poulton believes that a more feasible explanation is that all this variety of colouring enables "each bird to know its own eggs." But, if this is necessary in the case of Guillemots' eggs, how do Terns and Gulls, which nest together in such dense numbers, dispense with a similar provision? Most of the eggs of any one species are very much alike, and are so difficult to see that the greatest care must be taken by anyone visiting their nesting stations in order to avoid treading on them.