The scarlet ibis (Eudocimus ruber) is an unmistakable wading bird renowned for its spectacularly bright plumage, which stands out against the green and brown tones of its wetland habitat. This medium-sized bird is a member of the ibis family, Threskiornithidae, and is one of the only wading species to exhibit such an intense red coloration. Native to the tropical regions of South America and the Caribbean, the scarlet ibis is a highly social species, often seen foraging and flying in large, vibrant flocks. The species holds cultural significance in its native range, notably being one of the two national birds of Trinidad and Tobago.
Physical Characteristics and the Origin of Its Color
The adult scarlet ibis is almost entirely covered in vivid, luminous orange-red plumage, except for the tips of its longest flight feathers, which are deep, glossy black. Like other wading birds, it has a long, slender neck and long, thin legs. Adults typically measure 55 to 63 centimeters (22 to 25 inches) in length with a wingspan of approximately 54 centimeters (21 inches).
A defining feature is the long, thin, and distinctly down-curved bill, which the ibis uses for foraging. Males are generally slightly larger than females and possess a longer bill. The brilliant scarlet color is not a genetic pigment but is derived from the diet, specifically the consumption of organisms rich in carotenoids. The primary carotenoid responsible for the red hue is astaxanthin, obtained from crustaceans, such as small crabs and shrimp.
This dietary mechanism means the color is not present at birth; newly hatched chicks are altricial and covered in dull, grayish-brown down. The color change begins during the juvenile’s second molt, around the time it starts to fly, and gradually increases in intensity over a period of about two years. If the diet of the ibis becomes deficient in these pigments, as can happen in captivity, the plumage will fade to a pale pink.
Natural Habitat and Range
The scarlet ibis is native to tropical South America and parts of the Caribbean. Major populations are found along the coasts of Venezuela, Brazil, Colombia, Guyana, Suriname, and French Guiana, as well as on Trinidad and Tobago. The species favors wetland environments where food sources are plentiful.
These habitats include coastal marshes, expansive mudflats, and dense mangrove swamps, which provide rich foraging grounds and safe roosting sites. The ibis also utilizes shallow lagoons and brackish estuaries. While not strictly migratory, the species is highly nomadic, undertaking seasonal movements within its established range. These shifts are typically related to changes in water levels and food availability.
Diet and Foraging Behavior
As a carnivore, the diet of the scarlet ibis consists predominantly of small aquatic invertebrates. Preferred prey includes small crustaceans like shrimp and fiddler crabs, which are abundant in marshy habitats. The birds also consume aquatic insects, mollusks, small fish, and occasionally small snakes.
The ibis employs a specialized foraging technique for finding food in the soft substrate. It wades through shallow water or mud, using its long, sensitive, decurved bill to probe and sweep through the silt. This probing motion allows the bird to locate prey by touch rather than sight.
Lifecycle and Conservation Status
The scarlet ibis breeds in large, communal colonies, often nesting alongside other wading species like herons and egrets. Mating pairs construct simple platform nests of loose sticks, built high in the protective canopy of waterside mangrove trees or on islands. This colonial nesting behavior offers safety from predators.
The female typically lays a clutch of three to five eggs, incubated by both parents for 19 to 23 days. The chicks are altricial, and both parents share the duties of feeding and guarding the young. Young birds begin to fledge around 35 to 45 days after hatching and become independent at approximately 75 days old.
The species is currently classified as Least Concern by the International Union for Conservation of Nature (IUCN) on a global level, indicating its total population remains relatively large. However, the scarlet ibis faces several localized threats. Primary dangers include habitat loss and degradation resulting from coastal development, agriculture, and pollution of estuarine environments. Illegal hunting, the pet trade, and egg collection also pose risks to specific populations.