Although most birds incubate their eggs by sitting on them, a few species have found ways to relieve themselves of the chore. One of the most ingenious methods has been perfected by the mound birds or megapodes of Australia, the East Indies and adjacent areas.
These birds scratch together a large pile of sticks, leaves and dirt, lay their eggs near the top of the mound, and then cover them. The heat from the sun and the heat generated as the vegetation decomposes hatches the eggs.
Several birds use the same place year after year, building a community incubator, so that some of the mounds are fourteen or fifteen feet high and thirty to thirty-five feet in diameter.
The crocodile bird of Africa makes use of a similar principle; it lays its eggs in the sand where they are hatched solely by the heat of the sun.