Feathers: Differentiation and adaptation
Feathers are also highly evolved in the differentiation of different feathers (primary and secondary wing, tail, inner and outer contour feathers, down and filoplume) as well as adaptations to meet different habitats due to the unequalled insulation properties of feathers which permit the Emperor Penguin (Aptenodytes forsteri) to be the only animal that can endure winter on the Antarcticice cap. Most birds have an oil gland near the base of the tail. The bird takes this oil with its beak and coats individual feathers to waterproof them and maintain their insulation. Other birds, including herons, parrots (Psittacidae) and toucans lack this gland and condition feathers with a fine talc like dust, powder-down, that is produced by the continuous fraying of the tips of special feathers. Cormorants and darters, spend a great deal of their time diving in water, their feathers are not waterproofed, permitting them to get completely wet. This is of advantage since it reduces buoyancy and they can dive deeper and more easily in pursuit of their fish prey. After foraging they stretch their wings to dry.