Why Do Flamingos Stand On One Leg?

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Flamingos always seem to be standing on one leg. It’s a little odd, but also impressive, when you consider that the birds’ legs are long and thin and most of their body weight is horizontally oriented. Even humans, vertically oriented with the bulk of our weight in line with our center of gravity, have a hard time standing on one leg for more than a few minutes (most of us, anyway). One would think that if the birds are doing something so difficult so often for so long, there must be a benefit to it, but for a long time we had no idea what that might be. Scientists had proposed a number of explanations, but very few of them were ever tested.

Psychologists and flamingos seem like an unlikely pair, but Matthew Anderson, an Assistant Professor at the Department of Psychology at Saint Joseph's University in Philadelphia, studies the evolution of behavior, and he thinks the birds’ social nature makes them a good species for investigating social influences on behavior.

In one study, he found that whether an individual flamingo lays its head on the left or the right side of its back while resting is strongly influenced by the flamingos around it. Most birds prefer to rest their necks to their right, and this kind of laterality plays a role in the social cohesion of the flock. Given that, you might predict that left-leaning flamingos would have trouble getting along with the group, and Anderson’s results indeed showed that flamingos preferring the left were more likely to be involved in spats with their flockmates. Several other of his studies have similarly demonstrated the powerful influence that the flock has on the behavior of any one flamingo.

A few years ago, Anderson and his student Sarah Williams turned their attention to the opposite end of the flamingo and decided to see if the birds had a preference for their right or left foot while standing and resting, and if there was also a social influence there. While preparing for the study, they realized that no one had ever tested a more basic question: not if or why flamingos favor one leg over the other, but why flamingos favor one leg over two.

Two of the more popular explanations proposed for the one-legged posture are that it either reduces muscle fatigue or helps regulate body temperature.

The first hypothesis suggests that standing on one leg or the other prevents the muscles in both legs from getting stiff or tired at the same time. That way, if a predator comes along and a flamingo needs to make a break for it, at least one leg is ready to go and the bird can get moving faster. The other explanation is based on the fact that legs and feet account for a significant source of heat loss in birds. Keeping one leg or the other tucked up against the body, then, would conserve more body heat and help maintain a normal temperature.

Bird Watching

With their study having changed gears, Anderson and Williams went to the Philadelphia Zoo to observe its flock of Caribbean Flamingos. They spent several months watching the birds, each of which has a leg band that allows individuals to be identified. To evaluate the muscle fatigue hypothesis, the researchers timed how long it took for the birds to start moving after standing on one leg versus both legs. If that explanation was correct, the flamingos should have taken their first steps faster from a one-legged stance, but Anderson and Williams found that their movement was consistently faster (by about 14 seconds) when they’d been resting on both legs.

To test the heat retention idea, the researchers noted the temperature and weather conditions when the flamingos were resting on one leg or two. They found that more birds stood on one leg when they were standing in water than when they were on dry land, and that more birds would stand on one leg when it was cooler and on two when it was warmer, suggesting that one-legged resting helps in regulating temperature.

At first, the idea that a bird that usually lives in warm tropical climates would need to do anything special to hold onto its body heat seems a little counter-intuitive. Keep in mind, though, that flamingos spend most of their time in the water. As we learned before, body heat escapes more rapidly into water than air, and even in warmer climes, water can pull heat away from a body very quickly. “With greater body surface area submerged under water, resting on two legs would result in significantly more heat loss than resting on one,” the researchers say in their study.

Temperature regulation appears to be a key reason for the flamingos' iconic stance, but the psychologists aren’t ruling out an additional explanation, also tied to water. Given the amount of time they spend wading, Anderson and Williams write, the one-legged position might also help reduce flamingos’ exposure to fungus or parasites in the water.

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July 6, 2012 - 6:23am
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