Why are flamingos pink?

Flamingos are pink because of what they eat. Their diet of tiny plankton, both plant and animal, is loaded with carotenoids: the yellow, orange and red pigments that also colour carrots, tomatoes, salmon and shrimp. Enzymes in the flamingo's liver break those carotenoids down into the pigments that end up in its feathers.

Here is the twist. Animals, flamingos and humans included, mostly can't make carotenoids themselves. Plants, algae and a few bacteria and fungi do. So every bit of pink has to be eaten. Flamingos that feed directly on blue-green algae end up darker than those that get their pigment second-hand, by eating small animals that ate the algae.

You can watch it happen in a single bird's life. Flamingo chicks hatch in greyish plumage and only become light pink to bright red as adults, as pigment from their food builds up. The shade also varies by species: American flamingos are a brighter red because their food offers more beta-carotene, while lesser flamingos swallow less of it and stay paler.

Zookeepers have to plan for this. Even well-fed captive flamingos can fade to a pale pink if they don't get carotene at levels similar to the wild. And in the wild, colour is a message. A vivid flamingo is a well-fed, healthy one, and a more desirable mate. A white or pale flamingo is usually sick or malnourished.