SOME BIRDS' NESTS 145 



attempt no answer, while those who try are far 

 from being at one. 



Some naturalists of great authority have 

 recently adopted the theory that the young bird 

 lays up a mental picture of the nest while still 

 an inmate of it, and from this picture works when 

 its own nest -building time comes, and they sup- 

 port their theory by relating some very curious 

 facts regarding the behaviour of birds hatched 

 out in captivity. Broadly, these are to the effect 

 that a wild bird hatched out by, say, a canary 

 will, if it subsequently mates, fail to make the 

 nest of its kind, even if supplied with the right 

 material. Its ideas are hazy : it fumbles with 

 the building stuff, and the thing it ultimately 

 contrives is a mere generalized sketch of a nest, 

 lacking in every distinctive detail. Hence, it is 

 argued, instinct prompts the nest -making ; but 

 without actual knowledge of nests acquired by 

 the individual bird it cannot do more. And as 

 building birds do not gladly tolerate onlookers, 

 it is assumed that the year-old bird must work 

 on a memory of the nest in which it was reared. 



At present the hedges are full of the nests of 

 blackbirds and thrushes, both interesting specimens 

 of avian architecture, and both capable of throw- 

 ing some light on the question raised. Though 

 not precisely pretty, the nest of the mavis is one 

 of the neatest and least haphazard of the nests 

 built by British birds. Its plan, moreover, is 

 adhered to with an unvarying rigidity over an 

 immense area. Wherever the bird occurs in the 

 Old World the nest has the same marked charac- 



