CUCKOO. 301 
lierited 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. 6 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 6 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, yellow! ammer, 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 . Trav&s, vol. Ixxviii., p. 221 et seq, 
2 The young cuckoo is generally hatched first. 
