Observations on the Cuckoo. 447 
they also vary considerably in size, weight, 
and colour. It sometimes happens that two 
are deposited in the same nest, and cuckoos’ 
eggs are frequently hatched in the nests of 
other birds, after the birds that laid them 
have disappeared. 
There is certainly, Mr. Jenner observes, 
no reason to be assigned from the formation 
of the cuckoo, why, in common with other 
birds, it should not perform the several 
offices of nidification, of incubation, and of 
rearing its young; for it isin every respect 
perfectly formed for collecting materials and 
constructing a nest : neither its external shape 
nor internal structure prevent it from hatch- 
ing its eggs: nor is it by any means incapa- 
citated from bringing food to its young. To 
what cause then, he inquires, must we attri- 
bute the singularities of this bird ? May they 
not be owing to the following circumstances ? 
The short residence it is allowed to make in 
the country where it is destined to propagate 
its species, and the call that nature has upon 
it, during that short residence, to produce a 
numerous progeny. ‘The cuckoo’s first ap- 
pearance in Gloucestershire is about the mid- 
dle of April, commonly on the 17th: its egg 
is not ready for incubation till some weeks 
after its arrival, seldom before the middle of 
