Birds in general lay their eggs in nests, but such as are
disqualified for flight, as the partridge and the quail, do not lay
them in nests but on the ground, and cover them over with loose
material. The same is the case with the lark and the tetrix. These
birds hatch in sheltered places; but the bird called merops in
Boeotia, alone of all birds, burrows into holes in the ground and
hatches there.

Thrushes, like swallows, build nests of clay, on high trees, and
build them in rows all close together, so that from their continuity
the structure resembles a necklace of nests. Of all birds that hatch
for themselves the hoopoe is the only one that builds no nest
whatever; it gets into the hollow of the trunk of a tree, and lays its
eggs there without making any sort of nest. The circus builds either
under a dwelling-roof or on cliffs. The tetrix, called ourax in
Athens, builds neither on the ground nor on trees, but on low-lying
shrubs.



The egg in the case of all birds alike is hard-shelled, if it be
the produce of copulation and be laid by a healthy hen-for some hens
lay soft eggs. The interior of the egg is of two colours, and the
white part is outside and the yellow part within.

The eggs of birds that frequent rivers and marshes differ from
those of birds that live on dry land; that is to say, the eggs of
waterbirds have comparatively more of the yellow or yolk and less of
the white. Eggs vary in colour according to their kind. Some eggs
are white, as those of the pigeon and of the partridge; others are
yellowish, as the eggs of marsh birds; in some cases the eggs are
mottled, as the eggs of the guinea-fowl and the pheasant; while the
eggs of the kestrel are red, like vermilion.