Barack Obama pardoned two turkeys on Wednesday morning, as part of a long-standing White House tradition. According to a tweet from Mark Knoller of CBS News, Obama then asked, "Can somebody explain to me what the whole wattle thing's about?" Good question, Mr. President.
A bird's wattle, like its comb, can help to dissipate heat. The thin, elastic protuberances that hang down from a turkey's lower jaw allow for the rapid transfer of energy across the skin. Birds don't have any sweat glands, and most of their bodies are covered with a thick and well-insulating coat of feathers. When it gets really hot out, blood flow increases to those parts of their bodies that are exposed to the air, like the wattle, the comb (a growth at the top of the head), the snood (flaps of skin hanging over the bill), and the feet. Birds can also cool off by expelling water vapor. That is to say, they pant like dogs.
Wattles may be cool, but they're also manly. Male turkeys and chickens have larger and brighter wattles than females, and the size of the protuberance varies with testosterone levels. This gender dimorphism is strikingly displayed among those unusual chickens (about 1 in 10,000) that develop as male on one side of their bodies and female on the other: The masculine half of the wattle hangs much lower. Environmental factors can also affect wattle size. A male bird, for example, might experience wattle shrinkage after losing status in his social group.
Initial research on chickens, turkeys, and their ilk found that hens strongly prefer a male with a big and colorful comb but don't seem so turned on by the size or floppiness of his wattle. That doesn't mean the latter is irrelevant to sex: Male birds of some species engage in a wattle-shaking courtship dance called "tidbitting." This includes three distinct head movements—the "twitch," the "long bob," and the "short bob"—along with the emission of various noises and the repeated picking up and dropping of a morsel of food. Although hens are drawn to these displays on their own terms, wattles seem to make the dance even more attractive.
In 2009, a team of scientists in Australia demonstrated this fact by presenting two dozen Sebright hens with a series of computer-animated videos. In some cases, a virtual male was shown tidbitting with a normal wattle; in others, the wattle was either absent, rigid, or extra-floppy. Then the researchers measured the female response to this turkey porn. (There are some video clips at the bottom of this write-up.) It turned out that the hens were more interested in the rigid and normal wattles, which seemed to make the whole tidbitting routine more conspicuous. According to the researchers, these protuberances served to enhance "signal efficacy" for the courtship dance, in the way mascara might enhance some flirty eye contact.
In any case, a wattle isn't always a good thing for a bird. Chickens kept in cold weather are most susceptible to frostbite in their wattles and combs. That's why some farmers engage in a practice called "dubbing": They slice off the bird's head appendages with a pair of sharp scissors.
Got a question about today's news? Ask the Explainer.
AP Video: President Obama Pardons a Turkey