The case

is similar in most other such animals; that is to say,
the majority of quadrupeds copulate as best they can, the male
mounting the female; and this is the only method of copulating adopted
by birds, though there are certain diversities of method observed even
in birds. For in some cases the female squats on the ground and the
male mounts on top of her, as is the case with the cock and hen
bustard, and the barn-door cock and hen; in other cases, the male
mounts without the female squatting, as with the male and female
crane; for, with these birds, the male mounts on to the back of the
female and covers her, and like the cock-sparrow consumes but very
little time in the operation. Of quadrupeds, bears perform the
operation lying prone on one another, in the same way as other
quadrupeds do while standing up; that is to say, with the belly of the
male pressed to the back of the female. Hedgehogs copulate erect,
belly to belly.