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Flamingo hows, wheres and whys: Pink; erectile tissue; one leg


Credit: Tamar Assaf; Wikimedia

Flamingos are a pretty underrated bird. But the more you dig, the more you discover how strange they are, from their limbs to their pigment to the erectile tissue in their mouths.

One of the most recognisable traits of this leggy bird is how it seems to prefer to stand on one leg– even when asleep – with what appears to be its knee bent backwards. This is actually its ankle and heel; the flamingo's knee is located much further up the limb, hidden underneath its feathers. The whole area from the ankle to the toes is actually a giant foot. The joint that looks like an ankle, right down the bottom, is actually the beginnings of the toes. So effectively half the flamingo’s legs are actually its feet, and the normal stance for a flamingo is on its tiptoes. This arrangement makes more sense when you see a flamingo chick, whose legs and feet are still developing.

Credit: Auntie Rain, Flickr

But why stand on one leg instead of two? Until a few years ago, no one could say for sure, but there had been suggestions made about how this could reduce muscle fatigue and assist in thermoregulation. The former theory suggested that by standing on one leg, the flamingo was preventing half of its leg muscles from stiffening and wearing out, so if a predator turned up, it could get moving very quickly. And the latter theory suggested that by keeping one leg up and close to its body, the flamingo could reduce heat loss. In 2009, psychologist Matthew Anderson from Saint Joseph's University in Philadelphia, who had been studying the behaviour of flamingos for many years, decided to test both theories.

Observing captive Caribbean flamingos (Phoenicopterus ruber), Anderson's team timed how fast they could get moving from both the unipedal and bipedal stance. He found that, contrary to what the theory suggested, the birds were just as fast to get moving when they started from either stance.

Anderson next tested the thermoregulation theory and found that while the flamingos generally preferred resting on one leg to two regardless of the temperature, the percentage of birds resting on one leg was significantly higher among birds standing in the water than among those on land. This suggests that they were trying to lessen the amount of body heat that gets lost very rapidly when they come into contact with water. Anderson also noticed a relationship between the weather conditions and the leg lifting: "We demonstrate a negative relationship between temperature and the percentage of observed birds resting on one leg, such that resting on one leg decreases as temperature rises", he reported in Zoo Biology. So it would appear that this peculiar habit came about to keep the flamingos warm when standing in the water to feed.

New flamingo parents transfer their pink pigment to their new chicks via crop milk. Credit: Lajuarezo; Wikimedia

Another interesting aspect of the flamingo is how it gets its pigment. Flamingos aren't born pink, they're born white, and they gradually get their pink pigment from their parents. Both parents regurgitate what's known as crop milk to feed their young chicks, and this acts as a pigment transfer. So often you'll see the colour of new flamingo parents begin to fade as their chicks turn pink. The pinkish hue comes from pigments called carotenoids, which are found in the blue-green algae and crustaceans that flamingos eat in the wild, or in the pellets fed to captive flamingos. The same process causes salmon to become pink. Flamingos even use this pigment in sexual signaling, according to a 2010 paper in Behavioral Ecology and Sociobiology by a team of Spanish researchers who discovered red and yellow carotenoid pigments in the flamingo’s preening oils, and that during mating season, these birds would secrete much more of these pigments, seemingly to enhance their colours.

Flamingos have erectile tissue in their beaks to assist with filter feeding. Credit: Dori; Wikimedia

Another study, published in Anatomical Record in 2006 by biologist Casey Holliday and professor of anatomy Lawrence Witmer from Ohio University, found erectile tissue in the flamingo’s beak. Flamingos are known for their odd way of eating – they stand in shallow water, and put their beaks in an almost upside-down position in the water to catch food as it floats by. Their tongues act like pumps that manipulate the water, squeeze the food out and trap it. When Holliday and Witmer constructed a 3D model of a flamingo’s head, they noticed large, oval-shaped masses of erectile tissue on the floor of its mouth and running along either side of its tongue. Just like the erectile tissue in a man’s penis, this stiffens when filled with blood – like when the head is tipped upside-down – and helps to strengthen and support the floor of the mouth and tongue when the flamingo is feeding. “We suspect this stabilises the mouth and tongue and helps with the peculiar way that flamingos eat,” said Witmer. “It’s an important new piece of the puzzle of flamingo feeding – frankly, a piece we hadn’t known was missing.”

So flamingos seem to have it all sorted out. Except when it gets really windy, in which case they could be in trouble of ‘blowing away’. A BBC article from earlier this year reported that Zoo keepers at Dudley Zoo in the UK spent half an hour trying to catch a flock of flamingos because they were worried they’d be blown away in the 48km/h winds. Not an easy task, when you’re dealing with a bird that is renowned for its aggressive behaviour – “The best approach is to corner them and then move them by putting a hand around their neck and another across their body – and believe me, that's much easier said than done,” Zoo curator Matt Lewis told the BBC. And the Queen of Hearts was just sitting at home...


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