Others have adopted fish as their chief food, and the osprey snatches its prey from the water with as much facility as a gull or a petrel; while the South American caracaras (Polyborus) have adopted the habits of vultures and live altogether on carrion.

In every great group there is the same divergence of habits.

There are ground-pigeons, rock-pigeons, and wood-pigeons,--seed-eating pigeons and fruit-eating pigeons; there are carrion-eating, insect-eating, and fruit-eating crows.

Even kingfishers are, some aquatic, some terrestrial in their habits; some live on fish, some on insects, some on reptiles.

Lastly, among the primary divisions of birds we find a purely terrestrial group--the Ratitae, including the ostriches, cassowaries, etc.; other great groups, including the ducks, cormorants, gulls, penguins, etc., are aquatic; while the bulk of the Passerine birds are aerial and arboreal.