defenceless birds, such as the Wren, Willow-Warbler, and Dipper.
IV. Nocturnal birds, e.g. Nightjar, Owl, have plumage which will conceal them during the day. At first sight the Barn Owl would seem to be an exception, but this species is much more retiring than most of the others, and hides away entirely out of sight.
V. The usually dull colours of the Accipitres may help these birds to escape the notice of their prey. Such an explanation is not very satisfactory, as they do not sit still and wait for their prey to approach them. But, as these birds are well able to take care of themselves, they might be expected to have brightcoloured plumage.
There are certain individual cases which are very difficult to explain:—
(a) Why is the common Swift (Cypselus apus) such a sombre-looking bird?
(b) Does the Cuckoo (Cuculus canorus) really mimic a Hawk? There are other members of this family which appear to mimic species which are not allied to them.
(c) How is the Egret (Ardea garzetta) protected? It is not large, and has pure white plumage. Is its beak a sufficient means of defence?
(d) Ruffs (Machetes pugnax) are adorned with variously coloured plumes about the neck. They go through a form of battle for the Reeves. Such characteristics are contrary to the rule of the family (Scolopacidæ) to which they belong. By way of explanation, Darwin[1] states that the males of this species are probably polygamous.
(e) The plumage of the hen Oriole (Oriolus galbula) and the Jay (Garrulus glandarius) is quite bright enough to be conspicuous. But they nest among the thickest foliage.
Just as the coloration of birds' plumage falls naturally into divisions depending upon the nesting habits of the species concerned, so also may their eggs be grouped on similar lines. And moreover, the less important divisions also correspond in both cases. But when we are considering eggs laid in open nests, it
- ↑ 'Descent of Man,' ch. viii.
