A cockatoo is any of 18 bird species that belong to the family
Cacatuidae, they differ from the true Parrot in that they have a
movable headcrest, a gall bladder, different arrangement of cartoid
arteries, different skull bones and their lack of the Dyck Texture. It
is the Dyck Texture that causes light to scatter giving so many
parrots their beautiful colors and has nothing to do with pigment. The
cockatoo shares many charcateristics of the true parrot such as a
zygodactyl foot (two toes forward, two toes back) and a powerful
curved beak.
The term "cockatoo" is from the Malaysian word for the bird, kakaktua,
which translates to older sister, kakak "sister", tua "old".
Brad