Cockatoo
Like most parrots, the cockatoos are made their nests in holes in trees, which they are unable to excavate themselves. These hollows are formed from decay or destruction of wood by branches breaking off, fungi or insects such as termites or even woodpeckers where their ranges overlap. In many places these holes are scarce and the source of competition, both with other members of the same species and with other species and types of animal. In general, cockatoos choose hollows only a little larger than themselves, hence different-sized species nest in holes of corresponding (and different) sizes.