CUCKOO. 301 



herited instinct, so that all the nests in a given locality 

 would attain to a higher grade of excellence. 



Leroy also says that when swallows are hatched out 

 too late to migrate with the older birds, the instinct of 

 migration is not sufficiently imperative to induce them to 

 undertake the journey by themselves. ' They perish, the 

 victims of their ignorance, and of the tardy birth which 

 made them unable to follow their parents.' 



Cuckoo. 



Perhaps the strangest of the special instincts mani- 

 fested by birds is that of the cuckoo laying its eggs in the 

 nests of other birds. As the subject is an important one 

 from several points of view, I shall consider it at some 

 length. 



It must first be observed that the parasitic habit in 

 question is not practised by all species of the genus 

 the American cuckoo, for instance, being well known to 

 build its nest and rear its young in the ordinary manner. 

 The Australian species, however, manifests the same in- 

 stinct as the European. The first observer of the habit 

 practised by the European cuckoo was the illustrious 

 Jenner, who published his account in the ' Philosophical 

 Transactions. 1 From this account the following is an 

 extract : 



The cuckoo makes choice of the nests of a great variety of 

 small birds. I have known its eggs entrusted to the care of the 

 hedge-sparrow, water-wagtail, titlark, yellowtammer, green lin- 

 net, and winchat. Among these it generally selects the three 

 former, but shows a much greater partiality to the hedge-sparrow 

 than to any of the rest ; therefore, for the purpose of avoiding 

 confusion, this bird only, in the following account, will be con- 

 sidered as the foster-parent of the cuckoo, except in instances 

 which are particularly specified. 



When the hedge-sparrow has sat her usual time, and disen- 

 gaged the young cuckoo and some of her own offspring from the 

 shell, 2 her own young ones, and any of her eggs that remain 

 unhatched, are soon turned out, the young cuckoo remaining 



1 Phil. Trans., vol. Ixxviii., p. 221 et seq. 



* The young cuckoo is generally hatched first. 



