Palm cockatoos (Probosciger aterrimus) are the largest of all parrots, ranging from 49 to 68 cm in height. They weigh 500 to 1100 g, with females ranging from 500 to 950 g and males ranging from 540 to 1100 g. Wing length is around 35.1 cm, tail length 23.8 cm, bill length 9.1 cm, and tarsus length averages 3.5 cm. Palm cockatoos are almost all black with a 15 cm erectile crest on their head. Their beaks never close completely, always revealing a bit of their black-tipped red tongues. This partly open mouth makes it easier for the birds to hold nuts in their mouth and crack them at the same time. Their strong mandibles are used for cracking nuts and are larger in males than in females. Their legs are grey/black with few feathers on their thighs and their red facial markings are their most distinguished characteristic. Their cheek skin changes color based on their health or level of stress so when highly stressed the skin will change color to a pink/beige, while when highly excited the skin changes to yellow. In young birds, the underfeathers are lined with a pale yellow and in very young birds (under 18 months old), the tip of the bill and the eye ring are white.