The pinkness of flamingos is determined by food, but not by pink shellfish. The factors in the flamingo diet that ensure pinkness are carotenoid pigments, which are found in plankton, diatoms, and blue-green algae that the birds strain out of the muck in which they feed. The birds process yellow carotene into a red compound, canthaxanthin, which is stored in their legs and feathers.
If flamingos do not get enough of the right pigment, they lose their color when they molt. The color is important, because flamingos do not seem to breed successfully without it.
In captivity, they were once fed ground-up carrots and red pepper to keep them pink, but now zookeepers try to reproduce their natural diet or give them synthetic canthaxanthin.
Flamingos are not the only birds that change color with diet. “Red” canaries may be fed special nutrients to keep them red, though bird shows may frown on this color feeding. Cardinals also fade noticeably in winter, when they do not have access to their normal wide variety of foods.
Flamingos have very unusual feeding equipment. They eat with their heads upside down. The lower jaw contains a thick, fleshy tongue that moves back and forth to create powerful suction.
Both upper and lower jaws contain rows of projections called lamellae that meet to create a strainer to filter out edibles as water is pumped past them by the tongue. The projections range in size from large hooks to a Velcro-like fringe.
The greater flamingo, with larger lamellae, strains out and swallows small invertebrates, while the lesser flamingo, with a finer sieve, captures blue-green algae. The two species can feed side by side and eat different foods.