The stresses involved in landing and taking off, in running and in hunting mean that a variety of birds have relatively heavy and strong leg bones. Large raptors such as Eagles kill their prey with their feet and carry the prey considerable distances. When you look at a skeleton of an Eagle it is surprising how large the legs are. The fundamental bones of a bird's leg are the femur, fibula, tibiatarsus and tarsometatarsus. These are also called the femur, tibia and tarsus respectively in an external view of a bird's anatomy.
Most birds have four toes.
The fifth toe is lost completely except in some birds where it has become a defensive spur, such as the chicken. The exact number of toes and their arrangement, as well as their proportions, varies from family to family with Ostriches having only 2 toes, while Rheas and Emus have three. The foot is a very important appendage for a bird being the only source of support when standing, walking and running on a variety of surfaces. It also is a means of propulsion in aquatic species, a major weapon in many predatory species and for some birds their equivalent of a hand, functioning to grasp and hold objects the bird wishes to manipulate, mostly during feeding. The size and shape of the claws and the way the toes are arranged as well as the length of the toes and the degree of webbing are all dependent on what a bird uses its feet for and where it lives.