From the BBC:
Why flamingos stand on one leg
Editor, Earth News
Staying cool, or keeping warm?
It is one of the simplest, but most enigmatic mysteries of nature: just why do flamingos like to stand on one leg?
The question is asked by zoo visitors and biologists alike, but while numerous theories abound, no-one has yet provided a definitive explanation.
Now after conducting an exhaustive study of captive Caribbean flamingos, two scientists believe they finally have the answer.
Flamingos stand on one leg to regulate their body temperature, they say.
Matthew Anderson and Sarah Williams are comparative psychologists based at Saint Joseph’s University in Philadelphia, US who are interested in the studying the evolution of behaviour. …
To investigate, Anderson and Williams spent several months observing the habits of captive Caribbean flamingos (Phoenicopterus ruber) at Philadelphia Zoo, Pennsylvania, each of which carries a leg band that allows individuals to be identified.