I hope no one told our chickens that I am blogging about white meat and dark meat this week. They seemed a little slow out of the gate when I opened the chicken coop this morning; leery and suspicious, I thought.
Each morning I talk to the chickens as though we were all in the Royal Navy. “Good morning and I hope I find you well. Some eggs, if you please.” Then, in the evening when putting them to bed, I give them some Shakespeare, “We are such stuff as dreams are made on, and out little life is rounded with a sleep.” Although, come to think of it, last night I gave them something different. “For God’s sake, let us sit upon the ground and tell sad stories of the death of kings.” Perhaps that disturbed them and made them wonder.
Or maybe it was the Border Collie puppy, who seems to me to take an unhealthy interest in the chickens. As I said last time, the chickens are in no danger from the humans around here, but they worry some about the dogs. Dogs don’t discriminate between dark and white meat.
Unlike chickens and turkeys, most birds can’t afford the luxury of white meat.
What we call “meat” is, in fact, muscle tissue. To be precise, skeletal muscle tissue. Composed of cells that contract when they receive an electrical impulse, these are “voluntary” muscles and are the prime movers of birds and mammals. Attached to bones, they literally move the animal world by contracting and relaxing.
Two types of voluntary muscle tissue do all this work, “slow-twitch” and “fast-twitch.” Dark meat, actually red meat, is slow-twitch muscle tissue, full of red blood cells and mitochondria which ensure a rich supply of blood and oxygen. These are the muscles that contract more slowly and less often, but are responsible for all sustained muscular effort, such as flying.
Birds that fly a lot haven’t got room for much fast-twitch (white) muscle tissue. Hummingbirds, for instance, have no white meat at all. Only ground dwelling birds (Mostly ratites) and birds like chickens, turkeys, and grouse which fly rarely and only for short distances have the luxury of a lot of white meat, because fast-twitch muscle tissue has many fewer red blood cells and cannot provide the oxygen necessary for sustained effort.
That is why ducks and geese have little white meat; even their breast meat (the pectoralis muscle) is dark. Ducks and geese have to fly for long distances and need slow-twitch, endurance muscles. Besides, it kept them safe from my parents who, like I said last time, didn’t care for dark meat and lied to me about it.
One thing that fast twitch (white) muscles are good at is sudden movement. Gallinaceous birds (turkeys, grouse) are capable of sudden bursts of flight. (What birder hasn’t been startled by a grouse exploding into flight in front of her?) Birds that don’t do sustained flying don’t need as much of the heavier, redder muscle tissue which is why the pectoralis muscle tissue(breast meat)of chickens and turkeys is white.
In wild turkeys, about one-fifth of the muscle tissue is white. And we humans fool with the genes of domesticated birds just to increase the amount of white meat. But even domesticated chickens and turkeys use their legs and thighs for sustained muscular effort and that is the reason their legs and thighs contain dark muscle tissue.
For more, see Evans and Heiser “What’s Inside:Anatomy and Physiology,” Chapter 4 of The Home Study Course of Bird Biology, 2nd ed., Cornell Lab of Ornithology.
For more on my childhood, see my autobiography, Bleak House, which I self-published under a pseudonym.