The scarlet ibis (Eudocimus ruber) is a species of ibis found in tropical South America and the Caribbean. Their brilliant red plumage makes them one of the most recognizable wading birds in these regions. Scarlet ibis have some specific habitat and dietary requirements that limit their range and determine where they can successfully feed.
Habitat
Scarlet ibis are found predominantly in coastal zones. Their breeding habitats are restricted to tropical brackish swamps, mangrove thickets, and isolated islands along the Atlantic coast of South America and the Caribbean.
The largest breeding colonies are in Venezuela and Colombia. Important nesting areas also occur in Brazil, on islands off the coast of Guyana, and in Suriname’s coastal swamps. Smaller breeding populations exist in Central America, Cuba, the Bahamas, Haiti, and Trinidad.
Outside of the breeding season, scarlet ibis may disperse along the coasts of northeastern South America and the Greater Antilles. Their range extends as far south as Rio Grande do Sul in Brazil. Rare vagrants have been spotted along the Gulf Coast of the United States.
Breeding Habitat
Mangrove swamps and estuaries provide ideal breeding conditions for scarlet ibis. These habitats consist of stands of red mangrove trees growing in saline and brackish coastal waters. The trees thrive in muddy soils and their stilt roots stabilize the substrate.
This environment provides protection from predators, and the mudflats and shallow waters offer rich feeding grounds. The ibis build nests high in the mangrove canopy, where they are sheltered from tidal fluctuations.
Foraging Habitat
Outside of the breeding season, scarlet ibis inhabit similar coastal wetland habitats, including intertidal mudflats, estuaries, marshes, swamps, and mangrove forests. Their bright plumage makes them easy to spot among stands of green mangrove leaves.
Areas where freshwater rivers meet the ocean are especially attractive foraging grounds. These brackish waters provide abundant fish, crustaceans, and other prey.
Diet
Scarlet ibis are carnivores who eat a varied diet of small fish, crustaceans, insects, mollusks, and other invertebrates. Their distinctive long, curved bills are perfectly adapted for probing into mud and shallow water to catch prey.
Foraging Behavior
Ibis use a variety of foraging techniques to take advantage of different food resources. One method is to probe their bills into soft mud or sand, feeling for items buried below the surface. They may shuffle their feet to stir up prey buried in the sediment.
Another technique is to stamps their feet in shallow water to alarm fish and crustaceans and cause them to swim up where they can be readily caught. Ibis may also stand still and wait patiently to ambush passing fish and other prey.
Preferred Prey
The specific composition of their diet varies based on habitat and food availability. Important prey items include fiddler crabs, mud shrimp, marine worms, snails, insects, small fish like minnows and killifish, and shrimp-like crustaceans called mysids.
In freshwater habitats, scarlet ibis consume crayfish, frogs, mollusks, and insects like dragonflies. On coastal mudflats, they take advantage of tidal fluctuations to feed on small invertebrates. And in mangrove swamps, the ibis prey on crabs, fish, and other creatures.
Feeding Adaptations
Several key adaptations allow the scarlet ibis to take advantage of shallow wetland habitats:
- Their long, narrow, curved bills are specialized for probing into mud, sand, and vegetation in search of food.
- Their tactile bill tips allow them to detect prey hidden in sediment.
- Their long legs allow them to stride through shallow water while hunting.
- Their long toes help them balance and walk over soft mud.
Breeding and Chick Feeding
One of the most intriguing aspects of scarlet ibis biology is their tendency to time breeding with seasonal peaks in food availability. This ensures there are adequate resources to feed rapidly growing chicks.
Breeding Season
Timing of breeding varies across their range based on local conditions. In Suriname and Venezuela, peak breeding occurs during the rainy season from May to August. At this time, heavy rains flood coastal mudflats and mangroves, concentrating fish into channels and ponds.
In Brazil, the largest colonies nest during the rainy months of November and December when outflow from the Amazon River provides nutrients. And in Colombia, breeding coincides with wet seasons in October to November and February to April.
Chick Feeding
Both parents share brooding and feeding responsibilities. Chicks are fed regurgitated food by the parents. The abundance of prey in coastal habitats during the breeding season ensures plenty of food to sustain the chicks through the rapid growth phase as they mature and fledge.
Chicks triple their hatching weight by the time they fledge at about three weeks old. The bright reddish plumage starts to emerge after a few days. This coloration results from pigments obtained through the prey they are fed by their parents.
Synchronized Breeding
Scarlet ibis demonstrate a high degree of breeding synchrony, with most eggs being laid within one week. Synchronized breeding is thought to reduce predation risk and help maximize food resources.
It can result in massive reproductive colonies. In Venezuela’s Isla de Aves Wildlife Refuge, over 100,000 pairs may nest together in mangrove trees when conditions are favorable.
Range and Habitat Declines
Wetland habitat loss and degradation have led to declines in scarlet ibis populations. Their reliance on specific nesting and feeding habitats makes them vulnerable to changes in hydrology and ecology.
Coastal Development
Expanding human settlement, drainage of wetlands for agriculture and aquaculture, pollution from petroleum activities, and overharvesting of mangroves are all threats. For example, over 80% of suitable mangrove habitat has been lost in some parts of Venezuela’s Orinoco Delta.
Reduced Freshwater Flows
Upstream water diversions, dam construction, and channelization of rivers have reduced freshwater flows into many coastal ecosystems. The resulting increase in salinity can change vegetative communities and fish populations that ibis rely on.
Vulnerability to Climate Change
Climate models predict sea level rise will dramatically alter coastal habitats worldwide this century. As sea levels encroach further inland, coastal mangrove forests are likely to be progressively destroyed. Ibis breeding colonies nesting in coastal mangroves may be severely impacted.
Conservation Actions
Protected areas with coastal wetlands provide refuge for scarlet ibis populations. Isla de Aves Wildlife Refuge and Morrocoy National Park in Venezuela harbor globally significant breeding colonies.
Wetland restoration, invasive plant removal, and management of freshwater flows could aid ibis habitat in some regions. Ongoing monitoring and habitat protection will be key to sustaining populations.
Conclusion
In summary, scarlet ibis rely on specific coastal wetland habitats like mangrove swamps to breed and feed. Their specialized diet consists of fish, crustaceans, insects, and other small prey taken in shallow waters and mudflats. Synchronized breeding allows large colonies to take advantage of seasonal peaks in food resources.
However, extensive habitat loss driven by human activities has put scarlet ibis populations at risk across their range. Protecting remaining coastal wetlands and restoring hydrological processes will be crucial for the conservation of this iconic species.
Scarlet Ibis Population Estimates
Country | Population Estimate | Breeding Sites |
---|---|---|
Brazil | 2,000-5,000 pairs | Ilha dos Cardos, Bahia |
Colombia | 5,000-10,000 pairs | Islas de Salamanca National Park |
Cuba | 100-300 pairs | CiƩnaga de Zapata |
Guayana | 2,000-4,000 pairs | Wia Wia Natural Reserve |
Suriname | 50,000-100,000 pairs | Wia Wia Natural Reserve, Coppename Monding Nature Reserve |
Trinidad | 100-500 pairs | Caroni Swamp |
Venezuela | 140,000-180,000 pairs | Isla de Aves Wildlife Refuge, Orinoco Delta |