Cockatoos belong to an order of birds known as Psittaciformes (parrots). Parrots are widely distributed across the southern hemisphere, reaching their greatest diversity in the tropical forests of South America. They range in size from tiny Buff-faced Pygmy parrot weighing only 10-15 g (0.3 to 0.5 ounce) to the large Hyacinth Macaw weighing 1400-1700 g (3 to 3.7 pounds). The Psittaciformes are divided into two families: Cacautuidae (cockatoos) and Psittacidae (lories and true parrots).
Twenty-one cockatoo species are currently recognized, most of them are large, stocky birds. The exception is the Cockatiel, which resembles a medium-sized parrot. Cockatoos are distinguished by the presence of a crest. Most have black, white or grey plumage and, unlike other parrots, lack violet, blue, green, or purple feathers. The pinks in the plumage of a number of species puts them among the most beautiful bird species in the world.
Cockatoos have a large robust bill and muscular tongue which combine to efficiently process seeds and nuts on which they feed. Fourteen Cockatoo species occur in Australia. These are widely distributed and at least one or two species are found in most areas. The most widespread species are Galah and Cockatiel. The Sulphur-crested Cockatoo is common in the tropical north and temperate south-east.
The crest is used to express mood. The crest is raised when the bird is excited (territorially or sexually, or frightened). Some species have spectacular crests, while in others, the crest is relatively short.
Like most parrots, Cockatoos nest in tree holes, and no nest as such is constructed. The egges of all species are all white, and numbers laid vary from one to six, depending on the species. The newly hatched young are naked, later downy, and tended by both parents. Many cockatoo species are gregarious outside the breeding season and, in Australia, may assemble in flocks of a thousand or more, but groups of 40 to 50 birds are more common. Fortunately, most species exist in sufficient numbers in the wild, rendering them relatively safe from extinction.