Glimpse a far-off flock of flamingos, and you’ll immediately notice their color—pink, caused by the carotenoids in their diet. Move in for a closer look, and you’ll probably pick up on another classic flamingo characteristic: They often stand on one leg.

This tendency has proven a little tougher to explain than the birds’ bright feathers. As New Scientist reports, some scientists believe that tucking one leg up helps flamingos conserve body heat. In one 2009 study, researchers found that Caribbean flamingos more often stood one on leg in water than on land; and a 2010 study suggested that the unipedal position was more common in colder temperatures. According to the radio show BirdNote, herons, ducks, and a variety of other birds also hang out on one leg to minimize heat loss through exposed limbs.

But that’s not the only theory behind flamingos’ balancing act. Other experts think it’s a way to save energy, not heat. “Believe it or not, flamingos are more stable for long periods of time on one leg than they are on two,” University of Exeter zoologist Paul Rose told BBC Science Focus. “This is because the ligaments and tendons in their legs can be locked in position—and that reduces any muscular effort to stay in one place.”

In a 2017 study, researchers found that flamingo cadavers could stand unsupported on one leg, but not two, suggesting that live flamingos need to activate more muscles (and therefore use more energy) to balance on two legs. They also found that live flamingos standing on one leg while resting sway very little, which seems to support the idea that they can maintain a unipedal stance without much effort to keep them steady.

In short, we don’t really have a definitive answer as to why flamingos stand on one leg. It could be to stay warm, to relax, or to do both. It’s also possible that scientists haven’t yet landed on the correct theory. While you’re waiting for the next break in the case, you can learn more about flamingos here.

[h/t BBC Science Focus]