200 BIRD BEHAVIOUR 



structure of the beak that this is in other cases 

 sometimes more hooked in the young than in the 

 adult, as in young Gannets and Herons ; and 

 incidentally it would be well to examine all young 

 Cuckoos available, to see if the non-parasitic species 

 were hollow-backed at first as well as the others. 



The old Honey-guides appear to associate with 

 the young when reared, and perhaps instruct them 

 unconsciously or otherwise ; Mr. Ivy found two 

 old and three young birds of the Scaly-throated 

 species (/. variegatus) together, of which only one 

 old bird would guide him. 



The parasitism of the Cow-birds is in a way 

 more instructive than that of the Cuckoos and 

 Honey-guides, because here the gradations of the 

 instinct can be very plainly traced. These birds, 

 which are among the most Finch-like of the Trou- 

 pials, having short thick bills, and being able to 

 live on dry seed which they crack in typical Finch 

 fashion, are all closely related and easily recognizable. 



One of them, the original Cow-bird (Molobrus 

 -pecans) of North America, is as truly and com- 

 pletely parasitical as our Cuckoo, laying one egg in 

 the nests of various small insectivorous birds, which 

 rear that young bird alone, so that the others 

 evidently perish, even if not ejected ; a fate which 

 is likely to befall weak young birds in any case, as 

 exemplified by my Canary experience. This is a 

 glossy-black species with a sooty-brown head in the 

 male, brown in the female, and used to consort 

 with bisons when they were common, as it now 



