The 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. In fact, in general, birds have fewer bones than mammals or reptiles, so simply having fewer bones is an adaptation.

drawing of kiwi skeleton, from Richard Owen's 1841 monograph on Aptryx australis

Continuing your bird-meal, be sure to admire the large breastbone, highlighted in the above drawing. White meat of chicken and turkey breasts consists of the birds' powerful flight muscles. These strong muscles need solid anchoring, and that's supplied by the large breastbone. In wild birds, the more powerful the flier, the larger the breastbone. Flightless birds may lack breastbones altogether, as shown on the skeleton of the Kiwi at the right.

By the way, though flightless, Kiwis do have small vestigial wings, and if you look closely at the drawing you can see the bones.

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 (not needing free oxygen) instead of aerobic (needing free oxygen, supplied by blood in veins). White meat is white because it lacks blood veins.

Anaerobic breast muscles in ground-dwelling birds such as chickens and turkeys benefits the birds because they make brief spurts of flight to escape enemies, but don't fly high, or for long. During these short flights, the birds' white meat uses energy stored in the muscle tissue, in the form of the chemical glycogen. Glycogen is a polysaccharide that breaks down into glucose, which is exactly the simple sugar muscles need. For white meat, using that energy already stored in the muscle is faster than having oxygen pumped in through a network of veins, but the stored glycogen runs out fast, and is slow to replenish.

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 drawings you can't see the wishbone's Y shape because we are looking at it from the side.