1SS5.] Alle& on Sexual Selection and the Nesting of Birds. 1^7 



during incubation, on accozint of Iter bright colors. It seems 

 therefore needless and wholly gratuitous to resort to any theory 

 of sexual selection to account for the diverse methods of nest- 

 building among birds. Really, however, it is not the sitting 

 bird, in the case of open nests built in trees, whether she be bright 

 or dull-colored, or the contents of the nests, whether eggs or 

 nestlings, that lead to its discovery so much as the size and con- 

 spicuousness of the nest itself. Neither is the sitting bird herself 

 so much in danger as her charge, be it either eggs or nestlings. 

 The chief enemies of tree-nesting birds are squirrels, monkevs, 

 other aboreal mammals, and nest-robbing birds, to all of 

 which the nestling birds, particularly if very young, are as 

 welcome as the eggs, and in general they are much less conspic- 

 uous objects than are either the eggs or the sitting female. 



Now a word on another point. Mr. Wallace, and after him 

 Mr. Dixon and others, in discusing the question How do young 

 birds learn to build their first nest? claim that 'instinct' has noth- 

 ing to do with the matter, — that they learn by observation and 

 are guided by memory ! .Says Mr. Wallace: ;, It has, however, 

 been objected that observation, imitation, or memory, can have 

 nothing to do with a bird's architectural powers, because the 

 young birds which in England are born in May or June, will pro- 

 ceed in the following April or May to build a nests as perfect and 

 as beautiful as that in which it was hatched, although it could 

 never have seen one built. But surely the young birds before 

 they left the nest had ample opportunities of observing its form, 

 its size, its position, the materials of which it was constructed, 

 and the manner in which those materials were arranged. Memory 

 would retain these observations till the following spring, when the 

 materials would come in their way during their daily search for 

 food, and it seems highly probable that the older birds would 

 begin building first, and that those horn the preceding summer 

 would follow their example, learning from them how the founda- 

 tions of the nest were laid and the materials put together. Again 

 we have no right to assume that young birds generally pail- 

 together," etc. Mr. Dixon restates the case in much the same- 

 way. Alluding to 'blind instinct' as a factor in the case, he says: 

 ••To credit the bird with such instinct, which because it seems 

 so self-evident is taken to be matter of fact, is to admit that it 



