Birds
Scarlet Ibis
Eudocimus ruber · also called scarlet ibis, red ibis
The scarlet ibis is one of the reddest birds alive, a brilliant crimson wader that feeds across South American mudflats by day and pours back into mangrove roosts by the tens of thousands at dusk. Its colour is not fixed — it comes entirely from the crabs and shrimp it eats, and fades without them.
Overview
Scarlet ibises live in mangroves, mudflats, and coastal marshes of northern South America and Trinidad, probing for crabs, shrimp, small fish, and molluscs with a long downcurved bill. Adults are brilliant scarlet with black wingtips; juveniles start grey and white, gaining colour over about two years.
Colour from crustaceans
The red comes from carotenoid pigments in the crabs and shrimp it eats, deposited into growing feathers. Captive birds fed the wrong diet fade to pale pink or white within a year or two — which is why zoos add carotenoids to their food.
Mass roosts
Scarlet ibises roost and nest colonially, often with herons, and tens of thousands gather at dusk at sites like Trinidad’s Caroni Swamp and Venezuela’s Orinoco Delta — a major wildlife spectacle and the country’s national bird.
Status
The scarlet ibis is Least Concern globally, with large colonies still thriving, but declining in parts of its range from hunting, egg collection, and the loss of coastal mangrove habitat.
Scarlet Ibis: common questions
Why is the scarlet ibis so red?
The colour is built entirely from its food. Scarlet ibises eat large quantities of crabs, shrimp, and other crustaceans, and the shells and tissues of those animals contain carotenoid pigments, the same broad class of pigment that makes carrots orange and flamingos pink. The ibis absorbs these pigments during digestion, and its liver processes and deposits them into the keratin of growing feathers, producing the vivid red plumage over successive moults as the bird matures from its grey-and-white juvenile colouring. Because the pigment must come from the diet and cannot be made by the bird itself, an ibis moved to captivity and fed food lacking the right carotenoids will gradually lose its colour, fading to pale pink, orange, or even white within a year or two, which is exactly why zoos supplement captive ibis and flamingo diets with carotenoid additives to keep them looking natural.
Is the scarlet ibis the same species as the American white ibis?
This is genuinely debated among ornithologists. The scarlet ibis of northern South America and the American white ibis of the southeastern United States, Central America, and the Caribbean are extremely similar in size, shape, behaviour, and habitat, differing mainly in adult colour (scarlet versus white with black wingtips), and the two hybridise readily and produce fertile offspring where their ranges meet, notably in parts of Venezuela and Trinidad. Some taxonomists treat them as two colour forms of one species, Eudocimus ruber, while most current classifications keep them as separate species, Eudocimus ruber and Eudocimus albus, based on genetic and other differences, but the question is not fully settled and reflects how recently and incompletely the two lineages may have diverged.
Why do scarlet ibises gather in such enormous flocks?
Communal roosting and nesting in mangroves and small islands offers real safety benefits — predators such as snakes, raptors, and mammals find it much harder to approach or successfully attack a colony guarded by thousands of watchful birds than an isolated pair, and the sheer number of nests can overwhelm what predation does occur, so that most individual nests still succeed. Feeding is largely done separately across surrounding mudflats and shallows during the day, with birds streaming back in dramatic long lines toward the shared roost at dusk, a spectacle that has made sites like Trinidad's Caroni Swamp and Venezuela's Orinoco Delta major destinations for birdwatchers hoping to see tens of thousands of scarlet ibises arriving at once.
Is the scarlet ibis endangered?
Globally it is listed as Least Concern because large, healthy colonies persist, especially in Venezuela and the Guianas, and the overall population remains numerous. However, the species is in decline in parts of its range and has disappeared from or become rare in some areas where it once bred, due to a combination of hunting for meat and for the wild bird trade, egg and chick collection at colonies, and the drainage, clearing, and pollution of the coastal mangrove and mudflat habitat it depends on for both feeding and nesting. In Trinidad, where it is the national bird, the species is legally protected and the Caroni Swamp roost is actively managed as a protected wildlife sanctuary.