They have pink plumage due to their diet. In
fact, the flamingos feed on small aquatic microorganisms containing carotenoids, which color their feathers. Their beaks are specially adapted to separate mud and silt from the food they eat, and are uniquely used upside-down. The filtering of food items is assisted by hairy structures called lamellae which line the mandibles, and the large rough-surfaced tongue. Flamingos often stand on one leg, the other leg tucked beneath the body. The reason for this behaviour is not fully understood. Recent research indicates that standing on one leg may allow the birds to conserve more body heat, given that they spend a significant amount of time wading in cold water. However, the behaviour also takes place in warm water. As well as standing in the water, flamingos may stamp their webbed feet in the mud to stir up food from the bottom. Flamingos are very social birds; they live in colonies whose population can number in the thousands. These large colonies are believed to serve three purposes for the flamingos: avoiding predators, maximizing food intake, and using scarce suitable nesting sites more efficiently. Flamingos form strong pair bonds of one male and one female, although in larger colonies flamingos sometimes change mates, presumably because there are more mates to choose from. Flamingo pairs establish and defend nesting territories. They locate a suitable spot on the mudflat to build a nest (the spot is usually chosen by the female). It is during nest building that copulation usually occurs. Nest building is sometimes interrupted by another flamingo pair trying to commandeer the nesting site for their own use. Flamingos aggressively defend their nesting sites. Both the male and the female contribute to building the nest, and to defending the nest and egg. After the chicks hatch, the only parental expense is feeding. Both the male and the female feed their chicks with a kind of crop milk, produced in glands lining the whole of the upper digestive tract (not just the crop). Production is stimulated by a hormone called prolactin. The milk contains fat, protein, and red and white blood cells. (Pigeons and doves—Columbidae—also produce a crop milk (just in the glands lining the crop), which contains less fat and more protein than flamingo crop milk.) For the first six days after the chicks hatch, the adults and chicksstay in the nesting sites. At around seven to twelve days old, the chicks begin to move out of their nests and explore their surroundings. When they are two weeks old, the chicks congregate in groups, called "microcrèches", and their parents leave them alone. After a while, the microcrèches merge into "crèches" containing thousands of chicks. Chicks that do not stay in their crèches are vulnerable to predators.