Anatomy and physiology Birds -

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Anatomy and physiology Birds

Birds > Only the Birds
When a bird perches, its ankle bends and contracts the tendons in its foot, forcing its foot to close around the perch (B)
Bird musculature
Bird musculature

The skeleto-muscular system of birds combines light weight with high power for flight. Muscle mass is concentrated near the center of gravity-around the breast and bases of the wings and legs-which gives a compact, aerodynamic form. Long tendons control movements at the ends of the limbs. Flighted birds have more massive breasts and wing muscles; in terrestrial birds, much of the muscle mass is in the upper legs. In perching birds, the tendon from the flexor muscle loops behind the ankle; when the ankle bends on landing, the toes automatically close around the perch and maintain the grip without effort, anchoring the bird even in sleep.

In many species, the toe tendons have ridges, which also help to lock the feet around the perch. In contrast to the mammalian skeleton, birds’ bones are hollow and less massive and several have fused to form a strong, light frame. A bird’s skeleton constitutes only about 5% of its mass. Another distinctive feature is that the bones, including the skull, are pneumatized: their core is filled with air via a system of interconnecting passages that connect with the air sacs of the respiratory system and nasal/tympanic cavities. Flighted species tend to have extensive pneumatization but it is reduced or lacking in diving birds, which would be hindered by such buoyancy. Even birds’ bills are light-the horny equivalent of the heavy, toothed muzzle of mammals.

Bird skeleton
Bird skeleton
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