Chap. VII. 
OF THE CUCKOO. 
217 
she lays her eggs, not daily, but at intervals of two or 
three clays; so that, if she were to make her own nest 
and sit on her own eggs, those first laid would have 
to be left for some time unincubated, or there would be 
eggs and young birds of different ages in the same nest. 
If this were the case, the process of laying and hatching 
might be inconveniently long, more especially as she 
has to migrate at a very early period ; and the first 
hatched young would probably have to be fed by the 
male alone. But the American cuckoo is in this pre¬ 
dicament ; for she makes her own nest and has eggs 
and young successively hatched, all at the same time. 
It has been asserted that the American cuckoo occa¬ 
sionally lays her eggs in other birds' nests; but I hear 
on the high authority of Dr. Brewer, that this is a mis¬ 
take. Nevertheless, I could give several instances of 
various birds which have been known occasionally to 
lay their eggs in other birds' nests. Now let us sup¬ 
pose that the ancient progenitor of our European 
cuckoo had the habits of the American cuckoo ; but 
that occasionally she laid an egg in another bird's 
nest. If the old bird profited by this occasional habit, 
or if the young were made more vigorous by advantage 
having been taken of the mistaken maternal instinct of 
another bird, than by their own mother's care, encum¬ 
bered as she can hardly fail to be by having eggs and 
young of different ages at the same time; then the old 
birds or the fostered young would gain an advantage. 
And analogy w^omld lead me to believe, that the young 
thus reared would be apt to follow by inheritance the 
occasional and aberrant habit of their mother, and in 
their turn would be apt to lay their eggs in other birds' 
nests, and thus be successful in rearing their young. 
By a continued process of this nature, I believe that the 
strange instinct of our cuckoo could be, and has been, 
L 
