BIRD BONES
& MUSCLES
pigeon skeletonThe next time you're eating chicken or turkey and crack open a bone, pay special attention to its adaptations for flight. First of all, notice that relatively large bones such as those inside drumsticks are light and air-filled. Pork and beef bones in comparison are dense and solid. Some hollow bird bones are even equipped with cross walls, which provide extra strength, like internal struts in airplane wings.

A bird's horny bill is part of the skeleton, and even it, in view of the heavy-duty work it does, is amazingly thin and lightweight. It's significant that bird bills contain no heavy teeth. Fossils of the earliest birds do have teeth, like the birds' reptilian ancestors, so the lack of teeth is an adaptation reducing weight for flying.

Continuing your bird-meal, be sure to admire the large breastbone (highlighted in the drawing). White meat of chicken and turkey breasts is the birds' powerful flight muscles, the ones responsible for pulling wings downward against air, keeping the bird aloft. These strong muscles need solid anchoring, and that's the breastbone. In wild birds, the more powerful the flier, the larger the breastbone; flightless birds such as penguins lack breastbones altogether.

Have you ever wondered why white breast-meat is different from regular bird flesh? White breast-meat is composed of narrow, white muscle fibers that don't burn free oxygen for their energy, as regular muscles do. The technical way of saying this is that metabolism in white muscle fibers is anaerobic instead of aerobic. Anaerobic breast muscles in ground-dwelling birds such as chickens and turkeys is desirable because during these birds' brief spurts of flight to escape enemies (you never see these species soaring like songbirds), their circulatory system can't supply oxygen fast enough to the flight muscles. White muscle fibers are good for brief, very intense work, but they tire quickly.

While nibbling in the breast area, when you come to the curiously Y-shaped "wishbone," notice how it's positioned. The bone's "handle" projects forward to prevent collapse of the chest during flight. In the drawing you can't see the wishbone's Y shape because we are looking at it from the side.