Long-standing mystery solved: Why do flamingoes rest on one leg?

Long-standing mystery solved: ...
Researchers at Georgia Tech believe they've answered the long-standing mystery of why flamingoes stand on one leg
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If you had to rate the most comfortable positions to sleep in, standing on one leg is going to be right down the bottom of the list, just above standing on your head. But for flamingoes, snoozing while supporting their whole body weight on one stick-thin leg seems to be a natural first choice, and scientists don't really know why. Now, researchers at Georgia Tech believe they've cracked the case, and their finding could lead to better-balancing robots or prosthetic limbs.

It may seem like a simple question to ask a zookeeper, but why flamingoes stand on one leg for hours at a time has long stumped scientists. There are a whole flock of theories out there: maybe it's to regulate their body temperature in chilly water, or to keep their feet from pruning up like your fingers in the bath. Another suggests it makes them look like a reed from underwater so they don't spook their prey, while others assume flamingoes just find it more comfortable.

As it turns out, that last point is on the right track. The Georgia Tech team investigated the biomechanics of the birds, and found that this position requires no muscle activation, so the leg itself won't get fatigued after long periods of time. Millions of years of evolution has tuned the flamingo's anatomy to make the most of the pose.

"The biomechanics are such that when they stand on one leg, they become very stable and are able to maintain that posture without activating muscle," says Lena Ting, co-author of the study. "If they deviate from that posture to two legs, that no longer holds. It's very posture-specific, a one-legged posture that can support their body weight."

If you've ever wondered why the knees of birds seem to bend backwards, that's because the joint we see in the middle of the visible leg is actually the animal's ankle – the knee is hidden up under the wing. Previous studies have concluded that the ankle bones of flamingoes "lock" into place to keep the leg straight, but the Georgia Tech team found that the mechanism is more like a sling, and it helps create a "passively engaged gravitational stay apparatus."

The team studied juvenile flamingoes at Zoo Atlanta, but it was actually dead specimens and skeletons that provided the eureka moment for the researchers. A cadaver was stood up on one leg, and it stayed put by itself.

"Here we have a non-living animal able to stand on one leg," says Young-Hui Chang, co-author of the study. "Obviously, if it's not alive, then the muscles are not activated."

Along with unlocking this long-standing mystery, the researchers believe the lessons learned could be applied to robots and prosthetic limbs that can balance themselves more naturally and efficiently.

"If you design the biomechanics of a robot in the right way, not so much sensing but a sort of feedback control, then they would have this passive ability, and they would be more robust in uncertain environments," says Ting.

The paper was published in the journal Biology Letters.

Source: Georgia Tech

Idea falls apart when you consider that the *other* leg does require muscles to stay retracted. Seems more likely to do with the fact that birds sleep their brains in halves.
Imran Sheikh
so its a locking mechanism like eagles claws.. i feel the main reason is to appear like a tree growing out of water and reduce wind resistance while standing..
Douglas E Knapp
The other leg needs muscles to stay up and this does not answer what the natural advantage is to say sleeping like a goose on the ground. The question of why is clearly not answered. The only thing answered and only partly is how.
It's likely the bird have a way of locking the non weight bearing leg. This might be a good way to conserve energy for a robot but only when it's out of the wind in a perfectly still place where no one is going to bump it and knock it over. Still; it's easy to see the practical applications of the energy savings of 100 robots or 1000... etc. Another option is for the robot to hang on something and go limp.
Dave Brumley
Barn owls also sleep in this manner.
If one is observant, people also stand on one leg to rest, placing the other foot on the thigh, just above the knee, but often with a pole, spear or other upright, for additional support. This takes the load off of one leg entirely, and if correctly balanced, very little effort is required to remain upright. With both feet on the ground, then both legs have to be controlled, which requires more energy, more mental effort, which in turn is expensive in terms of energy.
Christopher commented on the idea 'falling apart' because muscles are needed to retract, lower the leg. Well, they never said there weren't any muscles in the legs, now did they! They simply stated that muscles were not needed to keep the leg locked in place.
This is the very reason modern birds--basically the only living descendants of dinosaurs-- can sleep while clutching tiny branches. Their feet don't need the muscles to be active while asleep. The feet 'lock in place', much like the Flamingo's legs.