The flamingo is well-known for its habit of eating with its head upside-down. This behaviour is largely due to the structure of its mouth and the logistics of lowering its long, graceful neck into the water. This behaviour allows flamingos to feed effectively in their natural habitat, but it has ramifications in other aspects of their lives.
Flamingos are filter feeders. They walk in the shallow, salty water and stir up the bottom with their long legs. The flamingo then leans its long neck down to the water and scoops up a mouthful of water, then closes its mouth and uses its tongue to force the water through comb-like extensions on the beak that allow the water to escape while retaining food to be swallowed.
The crustaceans and algae contain carotenoids that produce the birds' pink colouration. Because the flamingo must use its beak in an upside-down manner, the beak has evolved to reflect this. The flamingo's top beak functions like the bottom beak of most birds, and vice versa. Flamingos are among the very few animals that are able to move their top jaw while eating.