Flamingos’ signature pose is an enduring natural mystery. Scientists have proffered a number of theories about why the birds often stand on a single, slender leg while resting—some say it helps them conserve heat in cold waters, others maintain the stance reduces muscle fatigue. Now, a new study explores how the birds maintain their balancing act, providing new insights into the flamingo’s one-legged posture.
As Ed Yong reports for the Atlantic, biologists Young-Hui Chang of Georgia Tech and Lena Ting of Emory University wanted to find out how much muscle energy is expended when flamingos perch on one leg. They headed to Zoo Atlanta armed with a force plate, which measures the force that a body generates on the ground, and coaxed it under some fluffy juvenile flamingos. One flamingo fell asleep on the plate, allowing Chang and Ting to observe the little bird's surprising sturdiness as it slumbered. “Its body swayed less, and its center of gravity moved by mere millimeters,” Yong writes.
Chang and Ting then set out to conduct detailed examinations of the birds’ legs. They obtained two frozen flamingo cadavers from the Birmingham Zoo and dissected them, hoping to uncover features that would secure the leg joints in place. They found nothing of the sort. But when Chang decided to pick up the flamingo cadaver, the experiment took a dramatic turn.
He held the cadaver by its shin and hoisted it upright—and the leg joints instantly locked into a straight-legged pose. As Charles Choi writes for Discover Magazine, the dead bird’s ability to maintain a rigid leg prompted Chang and Ting to conclude that flamingos support themselves on one leg using a passive mechanism that does not require active muscle force.
“That was the ‘Aha!’ moment when we knew we were on to something special,” Chang told Choi. “If a dead flamingo could do it, then it is probably available for live birds to do.”
Intriguingly, the cadavers did not hold a stable pose when they were propped up on two legs, suggesting that standing on two feet requires more effort for flamingos than perching on one leg.
Why might this be the case? According to Travis M. Andrews of the Washington Post, flamingos’ unique skeletal structure helps them stay still while resting on one foot. Like humans, the birds have two main leg joints: the ankle and the knee. The bent crook of the leg that we can observe looks like a knee, but it is actually the birds’ ankle. Their knee is tucked up under the feathers of their belly. The researchers published their results in the Royal Society journal Biology Letters,
When flamingos start to snooze, they lift one leg, leaning slightly forward so their other foot is centered directly under their bulky carriage. This shifts the center of mass in front of the flamingos’ hidden knee, Yong explains in the Atlantic, pulling the hip and knee forward. The joints snap into place, and gravity keeps the birds standing still.
Matthew Anderson, an experimental psychologist who specializes in animal behavior, tells Paul Rincon of the BBC that Chang and Ting’s research is “a significant step forward." But, he adds, their study does not “examine when and where flamingos actually utilize the behavior in question, and thus this paper does not really address the issue of why flamingos rest while on one leg," Anderson said.
Still, Chang and Ting offer a guess. Writing in their study, the scientists suggest that flamingos may sleep on one leg simply because the pose requires less energy.