female cuckoo, which, according to most observers, lays at
least from four to six eggs, must pair with the male each time
after laying only one or two eggs. Now, if the cuckoo was
obliged to sit on her own eggs, she would either have to sit
on all together, and therefore leave those first laid so long,
that they probably would become addled; or she would have
to hatch separately each egg, or two eggs, as soon as laid:
but as the cuckoo stays a shorter time in this country than
any other migratory bird, she certainly would not have time
enough for the successive hatchings. Hence we can perceive
in the fact of the cuckoo pairing several times, and laying
her eggs at intervals, the cause of her depositing her eggs
in other birds' nests, and leaving them to the care of
foster-parents. I am strongly inclined to believe that this
view is correct, from having been independently led (as we
shall hereafter see) to an analogous conclusion with regard
to the South American ostrich, the females of which are
parasitical, if I may so express it, on each other; each
female laying several eggs in the nests of several other
females, and the male ostrich undertaking all the cares
of incubation, like the strange foster-parents with the
cuckoo.

I will mention only two other birds, which are very common,
and render themselves prominent from their habits.
The Saurophagus sulphuratus is typical of the great American
tribe of tyrant-flycatchers. In its structure it closely
approaches the true shrikes, but in its habits may be compared
to many birds. I have frequently observed it, hunting
a field, hovering over one spot like a hawk, and then proceeding