on the migration of birds. 29 
that the bird which had once crossed the Atlantic, or any 
other ocean, might have something impressed upon it that 
should prove an inducement to its return ; but this cannot be 
an incitement to the young one. The identical bird, which 
but a few weeks before burst from the shell, now unerringly 
finds, without any apparent guide, a track that leads it safely 
to the place of its destination, perhaps in many instances over 
the widest oceans. 
It is well known, that those birds which incubate several 
times in the course of one summer, forsake their first broods 
when they no longer require their protection : and being now 
alienated, they cannot, in their parents, find the guides that 
conduct their course. As swallows and martins congregate* 
prior to their departure from us, it may be said that their 
young, though discarded, may mingle with the common 
flock, and in this particular instance I am ready to admit that 
it is probable they may do so ; but there are many migrating 
birds that never either associate with swallows and martins, 
or join together in flocks, as the nightingale, redstart, and 
indeed the far greater number. As a striking proof that the 
parent bird cannot possibly be the guide, in one instance at 
least, we may point out the cuckoo, whose offspring finds a 
distant shore in perfect safety, although it could never know 
the parent to whom it was indebted for existence, and though 
* Swallows and martins congregate on the sunny sides of buildings for the sake 
of warmth, and not, as it is generally supposed, to hold a kind of consultation pre- 
vious to their final departure. In the wet summer of 1821, when the air was un- 
usually chilled by the long continued rains, they were observed to assemble, during 
some intervals of sunshine, for several successive mornings, as early as the middle of 
July; and in the present year (1822), I remarked the same on some mornings that 
were unseasonably cold about the middle of August. 
