For the Birds – Edibility of Birds and Gaudiness of Their Plumage

Most Thanksgiving meals center around a roasted turkey. On Thursday, you will be likely asked by the person carving the turkey if you would like dark or white meat. Apart from a difference in taste and texture, these two types of muscles differ in their physiology as well.

Domesticated turkeys and chickens have white muscles for the breast muscles, the largest muscles in the body. These muscles move the wings to provide the power stroke and the recovery stroke during flight. The drumstick and thighs have dark meat; these muscles are used for walking.

The difference between the two types of muscles lies in the basic function of muscle contraction. Dark muscle is mostly aerobic muscle; the muscles depend on oxygen to function. The dark color comes from a pigment called myoglobin that has a very high attraction to oxygen molecules. When blood flows through the capillaries of the muscles, the oxygen in the blood (carried by hemoglobin) is transferred to the myoglobin in the muscles. When oxygen becomes low in the muscles, oxygen is released from the myoglobin.

Aerobic muscles are efficient, making these muscles great for activities requiring endurance. On the other hand, they contract relatively slowly so are not effective in causing lightning-fast movements that might be used to avoid a sudden attack from a predator.

The white meat of a turkey or chicken has mostly anaerobic muscles. They work in the absence of oxygen. Such muscles have no need for myoglobin to store oxygen and the absence of myoglobin causes the muscles to appear white. These muscles are called fast-twitch muscles because they can contract very quickly. The disadvantage of these muscles is that they tire quickly as well.

If you have ever seen the meat of a game bird, you know that the breast is made of dark muscle. In fact, most birds have a predominance of dark muscle in their breasts. That dark muscle allows them to fly for long distances. They also have some fast-twitch muscle fibers to allow a rapid take-off or burst of speed. Our domesticated turkeys and chickens have mostly fast-twitch fibers in their breast muscles because of selective breeding.

Many species of birds are eaten by humans around the world. Some species have strong, disagreeable flavors while others are quite pleasing to the human palate.

In 1941, Hugh Cott, a biologist at Cambridge University, made an insightful observation while he was in Egypt preparing specimens of birds to take back to England. He noted that swarms of hornets were feeding readily on the skinned remains of a Palm Dove but avoided the flesh of a Pied Kingfisher (a bird with black and white plumage). Cott wondered if the striking plumage of the Pied Kingfisher was warning coloration, telling would-be predators that it would be a particularly distasteful meal. In a similar vein, the black and white fur of a skunk is considered to be warning coloration.

Cott set out to test his hypothesis that drab colored birds are tastier to a predator than birds with bold coloration. He gave the flesh of 38 species of local Egyptian birds to humans and asked for their opinion of the quality of the meat. The three species with black and white feathers were universally considered the least edible. The same flesh was presented to cats and hornets. Both species avoided the black and white birds as well. Cott continued his studies and suggested that the more vulnerable a bird is to a predator, the nastier its flesh tastes. Cott regarded brightly colored birds and slow moving birds as the most vulnerable. These distasteful birds seem to be relying on chemical defense, storing noxious chemicals in their flesh.

A fascinating variation on this chemical defense in birds comes from Papua New Guinea. In 1989, a graduate student named Jack Dumbacher, was conducting research on some birds of paradise. His research involved capturing birds of paradise in mist-nets so they could be banded for later identification. Other birds were captured as well in the mist-nets. One of the most common was a bright orange and black colored bird called the Hooded Pitohui. This species is known only from Papua New Guinea.

Dumbacher found the pitohuis give off a strong odor. Further, he discovered by accident that the pitohuis have a toxin in their feathers that causes a numbing sensation in a person’s mouth. Chemical analysis showed the chemical is a highly lethal compound called batrachotoxin, the same poison found in poison-dart frogs. Dumbacher suspects that the pitohuis are acquiring the toxin from their diet rather than making it themselves.

[Originally published on November 18, 2006]