Laura Erickson's For the Birds

This is the time of year when thoughts of birds run to dark meat versus light meat. Enough people prefer white meat, especially in these days of cholesterol anxiety, that poultry farmers are constantly developing supposedly improved strains of turkeys with bigger breast and smaller thigh muscles.

The white meat of turkeys and partridge is a unique adaptation arising from the fact that these birds spend the vast majority of their time walking about, and only rarely fly. They need a fairly constant and steady supply of rich, oxygenated blood to keep their legs moving. The muscle cells in their legs and thighs have a large supply of mitochondria and enough blood cells to darken the meat. To keep the blood supply to their legs adequate, they minimize the amount needed elsewhere, especially in their breast muscles, since turkeys and grouse don’t fly often. But when they do take off, it’s usually in a big hurry, when they’re in urgent danger. So the wing and breast muscles that power their flight are capable of a huge, but short, burst of energy. Anyone who’s ever heard the explosion of wings when a grouse takes off underfoot knows how powerful these wings are, thanks to that white muscle. But because there’s such a minimal supply of blood to these muscles, they quickly build up lactic acid and tire. That’s why it’s hard to flush a grouse twice, and almost impossible to flush it three times–the muscles are just too tired.

People are also suddenly examining those little bags of innards that we euphemistically call giblets. The liver and heart are pretty self explanatory, but what the heck is that gizzard for? Look at one carefully next time you’re preparing a turkey. If you have a completely intact gizzard, you can see the paired muscles. All the gizzard is is the lower chamber of the stomach, where food is pounded and ground up by those powerful muscles. The gizzard is capable of grinding up acorns, beechnuts, chestnuts, and other mast that the turkey swallowed whole.

All in all, Thanksgiving dinner can be an interesting study in anatomy as well as a delicious time for family and friends to celebrate the abundant riches we share. Of course, some people prefer not to think about biology right while they’re eating. Me, I’ve performed enough surgeries on turkeys in Gary Duke’s avian physiology lab that this Thanksgiving, I’m eating ham.