Most of a bird’s power production for flight occurs in the breast muscles. This mass of meat — pectoralis muscle for the powerful downstroke on top of the supracoracoideus muscle for the upstroke — is the subject of much attention at Thanksgiving.

Domestic turkeys have been bred to have disproportionately large breast muscles — so large, sadly, that their legs are not equipped to support them and they spend much time lying down. Male domestic turkeys are so lopsided that many commercial breeds can’t mount females for normal breeding, and artificial insemination is required.

But all birds, not just those selectively bred for our table, have outsized breast muscles. These flight muscles may comprise as much as 25% of their weight, whereas in humans, the comparable pectoralis muscles are closer to 1% of our weight.

Not only are turkey breasts large, but the flesh is white. This light-colored muscle is the result of fast-twitch muscle fibers that can contract rapidly to lift a massive turkey off the ground and get it up into the safety of a tree in emergencies. These fast-twitch fibers have less myoglobin, that cousin of hemoglobin that lives in the muscles.

The lack of myoglobin makes the meat whiter but also easily dried out during cooking. Any cooking regimen that blasts heat at white and dark meat for the same amount of time is guaranteed to be sub-optimal for one or the other. White meat has less myoglobin because these specialized muscle cells can contract repeatedly without oxygen, so an escape flight can happen much faster, without the need for immediate heavy breathing and oxygen replenishment that we are all familiar with after running up a flight of stairs too fast.

Wild turkeys have light meat in their breasts because they rarely fly, but when they do, it will need to be a quick, short burst of activity to escape a predator. Their thighs, on the other hand, will carry them steadily along for the rest of the day, and are thus made of dark meat, which has more myoglobin for carrying oxygen during sustained exercise.

Other game birds, such as ducks and geese — which are capable of sustained flights on a regular basis, especially during migration — have slow-twitch dark meat for breasts too, and this is why a lot of people prefer turkey meat to that of other game birds.

Most birds only have dark meat, because they spend their days flying from place to place using oxygen in a sustainable manner. Breast muscles of a typical songbird like a sparrow are large, comprising about 20% of the body mass. Like the engines in an airplane, these breast muscles power the wing flaps, forcing air to speed over the wing surface to create lift, just like the engine on a plane.

Dan Cristol teaches in the biology department at William & Mary and can be contacted at dacris@wm.edu. To discover local birding opportunities visit williamsburgbirdclub.org.

https://www.pilotonline.com/2025/11/24/birding-the-real-reason-people-eat-turkeys/