54 OBSERVATIONS ON THE CUCKOO. 
times happens that two are deposited in the same 
nest ; and Cuckoos’ eggs are frequently hatched in 
the nests of other birds, after the birds which laid 
them have disappeared. 
There is certainly, Dr. Jenner observes, no reason 
to be assigned, from the formation of the Cuckoo, 
why, in common with other birds, it should not per- 
form the several offices of nidification, of incubation, 
and of rearing its young. It is in every respect per- 
fectly formed for collecting materials and constructing 
a nest; neither its external shape nor internal struc- 
ture prevent it from hatching its eggs; nor is it by 
any means incapacitated for bringing food to its 
young. To what cause then, he inquires, must we 
attribute the singularities of this bird? May they 
not be owing to the followmg circumstances ?—The 
short residence it is allowed to make in the country 
where it is destined to propagate its species, and the 
call which nature has upon it, during that short resi- 
dence, to produce a numerous progeny. The Cuckoo’s 
first appearance in Gloucestershire is about the middle 
of April, commonly on the 17th; its egg is not ready 
for incubation till some weeks after its arrival, seldom 
before the middle of May; a fortnight is taken up by 
the sitting bird in hatching the egg; the young bird 
generally continues three weeks in the nest before it 
flies, and the foster-parents feed it more than five 
weeks after that period ; so that, if a Cuckoo should 
be ready with an egg much sooner than the time 
