When you're on the dating scene, conventional wisdom tells us it's a good idea to maintain your appearance. Flamingos know this, which is why they spend so much time smearing their necks with a secretion expressed by a gland on their rear ends.
Flamingos wouldn't be pink if they ate different foods. Many plants and algae produce compounds called carotenoids, which are the reddish pigments that give carrots, salmon, pumpkins and lobsters their warm hue. Flamingos dine primarily on brine shrimp, which in turn feed on algae rich in carotenoids. As a result, flamingo babies, which are gray or white at birth, eventually eat enough brine shrimp to turn their feathers pink within the first couple of years of life.
Although their diets color their feathers from the inside out, research focused on greater flamingos (Phoenicopterus roseus) in southern France and published in September 2021 in the journal Ecology and Evolution, finds that these ultrasocial birds smear their neck feathers with secretions rich in carotenoids that come out of the uropygial gland on their rump. The uropygial gland, also known as the preen gland or oil gland, is found in most birds and its oil is distributed through the plumage by means of preening. Flamingos preen with the especially carotine-rich oil they produce to prevent their beautiful pink plumage from bleaching in the sun — especially during breeding season, which is basically Met Gala season for flamingos. It's a little bit like applying rouge.
The researchers discovered a correlation between carotenoid concentrations inside and outside flamingo feathers, as well as the pinkness of an individual's feathers, and the concentration of pigments in their uropygial secretions. In other words, when birds stood out in the sun all day, their color faded, which was not the case for birds kept out of the sun. In order for the sun-bathing birds to maintain breeding-season-worthy color, they had to constantly apply makeup.
Maybe this is why a group of flamingos is called a flamboyance?