No. 78: Nov-Dec 1991
This profound question elicited a wide range of replies from readers of New Scientist, some of which are worth recording here.
W. Smith supposed that because the flamingo has exceptionally long, thin legs that it was difficult for its heart to return blood from its feet. Therefore, by standing on one leg and occasionally switching, the flamingo prevents blood from collecting in its feet.
L.J. Los replied with reference to a phenomenon of which we were unaware:
"Farm animals are well known for letting sleep be linked to half of their brain at a time. In this way they can maintain a measure of alertness -- even while looking fast asleep.
"Flamingos roost upon one of their legs while the other half of their body is in the sleep stage. When the other half of their brain and body earns a rest, they change legs. A leg that is in the sleep stage would not support the bird as a whole."
But P. Hardy had the best answer:
"Why do flamingos stand on one leg? So ducks only bump into them half the time."
(Various authors; "Flamingo File," New Scientist, p. 52, August 17, 1991.)