Eagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species (the Bald and Golden Eagles) can be found in the United States and Canada, nine more in Central and South America, and three in Australia.
Eagles differ from many other birds of prey mainly by their larger size, more powerful build, and heavier head and beak. Even the smallest eagles, like the Booted Eagle (which is comparable in size to a Common Buzzard or Red-tailed Hawk), have relatively longer and more evenly broad wings, and more direct, faster flight. Most eagles are larger than any other raptors apart from the vultures. Species named as eagles range in size from the South Nicobar Serpent-eagle, at 500 g (1.1 lb) and 40 cm (16 in), to the 6.7 kg (14.7 lbs) Steller's Sea Eagle and the 100 cm (39 in) Philippine Eagle. Like all birds of prey, eagles have very large hooked beaks for tearing flesh from their prey, strong muscular legs, and powerful talons. They also have extremely keen eyesight which enables them to spot potential prey from a very long distance. This keen eyesight is primarily contributed by their extremely large pupils which ensure minimal diffraction (scattering) of the incoming light.
Eagles build their nests, called eyries, in tall trees or on high cliffs. Many species lay two eggs, but the older, larger chick frequently kills its younger sibling once it has hatched. The dominant chick tends to be the female, as they are bigger than the male. The parents take no action to stop the killing.