COLOURATION OF BIRDS AND THEIR EGGS. 171 



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 da) r . 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 bright- 

 coloured 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) Buffs (Machetes pugnax) are adorned with variously 

 coloured plumes about the neck. They go through a form of 

 battle for the Beeves. Such characteristics are contrary to the 

 rule of the family (Scolopacidce) to which they belong. By way 

 of explanation, Darwin* 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 con« 

 spicuous. 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 con- 

 cerned, 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, 



