INTRODUCTION. xv 



tube. In Australia there is a very conspicuous black-and-white Pigeon 

 (Carpophaga luctuosa) which always, it is said^ prefers to build its slight 

 nest on a branch over water. How is it possible for even winged enemies 

 to take such a citadel by storm, or harm the parent safely swinging in her 

 wonderful cradle ? This is undoubtedly the true reason that these nests 

 are hung so conspicuously ; the eggs, the young, and the brooding (often 

 brightly coloured) parent are all equally safe in such a structure, where 

 concealment could serve no special end in shielding them from their 

 natural enemies. It seems also a most interesting fact that these domed 

 pensile nests are not always so conspicuous as might be imagined. As an 

 example, I will take the by no means brilliantly arrayed little Sericornis 

 citreogularis of Australia, whose nest is built in the dense and humid 

 forests, where the trees are covered with moss, often accumulated in large 

 masses at the extremities of the drooping branches. In these masses of 

 moss, or suspended to them, the little bird places its nest with so much 

 skill that it is impossible to say which are really nests, and which are mere 

 festoons of moss, until each is minutely examined. Our next group 

 consists of 



Birds in which both sexes are dull in colour, and which build 

 covered nests from motives of safety other than concealment. — I do 

 not think that the fact of dull-coloured females sitting in covered nests can 

 be taken as a serious objection to the law of bright-coloured females sitting 

 in covered nests; for, as Darwin remarks {' Descent of Man,' ii. p. 168), 

 other advantages may be gained irrespective of concealment, such as 

 shelter, greater warmth, or in hot countries protection from the sun, or 

 sudden changes of temperature, or, in the case of many domed pensile 

 nests built on slender branches, protection from certain enemies, as is the 

 case with the Indian Ploceus bay a, which makes the entrance to its bottle- 

 shaped pendulous nest inverted, so as to baffle the approaches of tree- 

 snakes and other enemies. Another explanation may be that these plain- 

 coloured birds of both sexes are the descendants of some showy ancestor 

 that built in a covered nest ; and this peculiarity has been transmitted to 

 an entire genus, and retained, even in cases where the plumage of the bird 

 has assumed a more sombre tint, through the laws of Inheritance. It js 

 easy to believe that if no direct and special cause for a change arises, the 

 nesting-economy will remain unchanged even if the plumage of the bird 

 or of any of its descendants changes to less showy tints. 



The Swift {Oypselus apus) and the Sand-Mar tin {Hirundo riparia) are 

 both dull-coloured birds, the sexes are alike, and they build nests concealed 

 in holes. But in these cases the colour of the plumage does not influence 

 the conditions of nidification. The Swift makes its rude nest in a hole, it 

 has, so far as we can determine, no means of protecting itself or its eggs 

 from enemies, and consequently retires to such a site where it can rear its 



