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White-faced Ibis

Order: Ciconiiformes
Family: Threskiornithidae
Genus/Species: Plegadus chihi

Description

The White-faced Ibis is a medium-sized (46-56 cm tall, 450-525 grams) dark wading bird with a 1 meter wingspan. Their rich brown plumage has metallic purple highlights on the back and shoulders and bronze and green tints on the wings and tail. They have long, slender decurved bills. The bare skin of the legs is grey most of the year, deepening to maroon in the breeding season. Breeding adults have red eyes. Juvenile birds have brown eyes and streaks of dirty white and pale brown in the plumage. The White-faced Ibis is distinguished from the very similar Glossy Ibis by a thin band of white feathers bordering the bare skin around the eyes and bill. This white plumage is most prominent in the breeding season. Males are slightly larger than females and have longer bills, but are otherwise identical in appearance.

Distribution and Habitat

White-faced Ibises breed locally from Mississippi to western Minnesota westward to California, Nevada, and southeastern Oregon. They inhabit marshes, swamps, and rivers, preferring freshwater wetlands. They migrate from the northern portions of their range in the colder months to winter as far south as northern South America. The breeding populations of the Texas and Louisiana coasts are year round residents.

Diet

Ibises will feed in large flocks of up to 1,000 birds. They utilize both natural wetlands and irrigated and flooded agricultural fields. Prey on the surface of the water or mud is located by sight. They also use their long sensitive bills to probe shallow water and mud feeling for prey. When they locate a prey item the bill snaps shut and they pull out their catch. They feed on earthworms, insect larvae, leeches, snails, crayfish, small fish, frogs, and bivalves.

Ibises often forage in association with taller wading birds such as herons or Great Egrets. The constant probing of the Ibis's bill may scare up prey for the heron that is out of the Ibis's reach. In return the Ibis receives extra warning of predators such as Peregrine Falcons or Red-tailed Hawks by taking advantage of the taller bird's wariness and larger field of view. When feeding in irrigated rice, barley, and hay fields they are often seen with flocks of gulls. This association is unlikely to benefit the Ibis as gulls are apt to steal their prey before they can swallow it.

Reproduction

The inland populations of White-faced Ibises prefer to breed in shallow freshwater marshes with islands of emergent vegetation such as cattails or bulrushes. The Louisiana and Texas populations also breed in salt marshes. They reach sexual maturity in their second year. Nest building and egg laying begins within weeks of the birds' arrival on their breeding grounds. Many pairs may utilize the same habitat, sometimes forming large colonies with little evidence of intraspecies aggression.

Courting birds vocalize to each other and engage in mutual preening and bill rubbing. Copulation occurs at or near the nest site. Both parents participate in building the cup shaped nest of small twigs lined with finer material. The nest is usually placed on top of emergent aquatic vegetation or in a low shrub or tree over the water. Locating the nests in or over water helps protect the eggs and nestlings from mammalian predators such as skunks, racoons, and long-tailed weasels. Nests are also preyed on by gulls, magpies, ravens, crows, owls, and grackles.

Three to four pale bluish-green eggs are laid. Both parents take turns incubating for 20-26 days. Chicks hatch sequentially, 1 to 2 days apart. The mostly bare pink skin of the altricial chicks is sparsely covered with fine dark down. Their short flesh-colored bills are marked by three indistinct black bands. Parents feed the begging chicks by dribbling regurgitated food into their upturned bills. The last chicks to hatch are usually outcompeted by older siblings and are likely to starve.

The chicks develop rapidly and by nine or ten days of age are able to wander a short distance from the nest. The first few weeks are spent hiding in vegetation near the nest, but by the end of week three they are actively exploring the immediate area. They make their first flight attempts with short glides at four weeks. They begin to take short flights from the colony at six to seven weeks of age and are believed to be totally independent by eight weeks old.

Conservation

Although White-faced Ibises were hunted legally until the early part of this century, their lack of showy breeding plumes meant that they were not as severely effected by shooting as were herons and egrets. They have been primarily threatened by habitat destruction and pollution. Population numbers declined precipitously in the 1960s and 1970s due to DDT contamination and accelerating habitat loss. The inland populations have rebounded somewhat in the last two decades thanks to the banning of DDT and improved habitat management on state and federal refuges. Coastal populations have continued to decline over the past 20 years perhaps due to the pesticides used in rice farming. The White-faced Ibis is being studied as a possible candidate for federal listing under the Endangered Species Act.


References

Ehrlich, P.R., Dobkin, D.S. and D. Wheye. 1988. The Birder's Handbook. Simon and Schuster, New York.

Ehrlich, P. R., Dobkin, D. S., and D. Wheye. 1992. Birds in Jeopardy. Stanford University Press, Stanford.

Farrand, J. Jr. ed. 1983. The Audubon Society Master Guide to Birding Vol. 1. Alfred A. Knopf, Inc. New York.

Netherton, J. 1994. At the Water's Edge: Wading Birds of North America. Voyageur Press, Stillwater, MN.

Ryder, R.A., and D.E. Manry. 1994. White-faced Ibis (Plegadus chihi) In The Birds of North America, No. 130 (A. Poole and F. Gill, Eds.) Philadelphia, PA. The Academy of Natural Sciences; Washington, D.C.: The American Ornithologist's Union.