Carotenoid Pigment
Flamingos have bright feathers and strongly hooked bills that make them easily recognizable. By nature however, flamingos are actually white. Their feathers range from white to deep pink depending on the amount of carotenoids they consume. Carotenoids are yellow, orange or red pigments synthesized by algae, fungi and bacteria. They exist in the algae and plants that flamingos and small crustaceans eat. The crustaceans, like shrimp, are rich in red carotenoid pigment; as flamingos consume these, their feathers gradually turn from white to vibrant, rich pink. The more shrimp and algae they eat, the more pink they become.
Crustaceans
Flamingos eat by wading into deeper water away from the edges of the lake where most birds look for food. They hold their beaks upside down in the water and eat by sucking water and mud in through the front of their bill before pushing it out the sides. In the process, they pick up many small crustaceans like shrimp and other tiny water creatures that they retain and consume. Caribbean flamingos are the largest of all flamingo types and consume the most crustaceans. Because of this, they are also the brightest of all flamingo types, displaying dramatic pink hues.
Algae
Smaller flamingos like puna flamingos, andean flamingos and lesser flamingos have smaller beaks with briny plates called lamellae. These lamellae function like miniature filters, trapping extremely small shrimp and fine particles like blue-green and red algae, which the flamingos consume. While these algae are also rich in carotenoid pigment, smaller flamingos are not as pink as their larger counterparts, as they do not consume the same quantity of crustaceans. Smaller flamingos have mostly white feathers rimmed with pink lines and a pink undercarriage.
Flies and Mollusks
Chilean and Caribbean flamingos are the largest of the species and therefore eat some foods that smaller flamingos cannot. In addition to crustaceans, they feed on invertebrates like brine flies, larger shrimp and mollusks. They can wade farther out into lakes and lagoons, and stick their heads deeper beneath the water's surface to reach larger prey. Sometimes, they swim out to the center of lagoons to feast upon larger invertebrates swimming there.