Stilts and Avocets: Recurvirostridae
STILTS AND AVOCETS: RecurvirostridaeBLACK-WINGED STILT (Himantopus himantopus): SPECIES ACCOUNTS
AMERICAN AVOCET (Recurvirostra americana): SPECIES ACCOUNTS
Stilts and avocets range from 14 to 20 inches (35 to 51 centimeters) in height and from 5.8 to 16.2 ounces (166 to 461 grams) in weight. All species have striking bill shapes. In avocets, the bills curve upward, particularly in females. The ibisbill has a bill that curves downward. In stilts, the bills are generally straight or slightly curved. Stilts and avocets have the longest legs (in proportion to body size) of any shorebirds. These may be red, blue, or gray in color. Most stilts and avocets are black and white in color, sometimes with reddish-brown areas.
Stilts and avocets are found worldwide, on all continents except Antarctica. The largest number of species occupy areas near Australia.
Most stilts and avocets occupy large wetland areas. The ibisbill, however, prefers rocky habitats along slow-moving streams. Avocets, as well as the banded stilt, generally live in saltwater wetlands. Other stilt species use both saltwater and freshwater wetlands. The Andean stilt occurs only close to high altitude saline lakes. Many stilt and avocet species also use man-made areas as habitat, including dams, irrigation sites, and sewer ponds.
Stilts and avocets eat aquatic invertebrates such as crustaceans, insect larvae, worms, and mollusks. They also eat small fish and, sometimes, plant material. Stilts and avocets generally obtain food by pecking at items. In addition, some avocets swing their bills through water or soft mud and filter out small food items. Some stilts and avocets also stick their entire heads underwater to look for food. The ibisbill uses its bill to rake through pebbles in the rocky stream habitats it prefers. It then snatches whatever small aquatic animals it disturbs. Finally, some stilts and avocets have been known to snap at flying insects.
BEHAVIOR AND REPRODUCTION
A few species of stilts and avocets, such as black-winged stilts, pied avocets, and American avocets, migrate from breeding grounds to wintering grounds over the course of the year. Ibisbills migrate altitudinally, moving from higher to lower elevations and back. In addition, most species move short distances to find suitable wetland areas.
Most species of stilts and avocets form large flocks while feeding. Flocks can include several thousand individuals. In most cases, feeding occurs during the daytime. However, some stilts also feed at night. Stilts and avocets generally roost, or spend the night, standing in water. They may also rest during the day, either sitting on the ground or standing on one foot with the head tucked under the wing. Unlike other members of the group, ibisbills are usually found alone, in pairs, or in much smaller groups that rarely exceed seven or eight individuals.
Except for the ibisbill, stilt and avocet species also nest in large colonies, groups, which may include multiple shorebird species. Breeding colonies tend to be very noisy. Stilts and avocets use a variety of calls to communicate with mates or offspring, or to signal danger.
CROSS-BREEDING IN AN ENDANGERED STILT
The black stilt, which is found exclusively in New Zealand, is endangered for a variety of reasons. Wetland habitats have been destroyed by humans, and mammals not originally found on New Zealand eat black stilt eggs. Black stilts also cross-breed, that is, mate with individuals of other species. In the case of black stilts, cross-breeding occurs with black-winged stilts, which are also found on New Zealand. There are now fewer than one hundred black stilts left in existence.
Most stilts and avocets are monogamous (muh-NAH-guh-mus), with a single male breeding with a single female at one time. Birds may change mates over the course of a breeding season, however. To attract females, males perform a display that involves dipping their heads, shaking, and then preening, or smoothing their feathers. After mating, the male and female cross bills and walk together, the male holding one wing over the back of the female. Generally, the female lays three or four eggs at a time. Both the male and the female participate in incubating, or sitting on the eggs, and feeding and protecting the chicks once they hatch. Adults dive-bomb potential predators and may also fake a broken wing in order to distract intruders and draw them away from the nest.
STILTS, AVOCETS, AND PEOPLE
There are no significant interactions between most species of stilts and avocets and people. However, humans have appreciated these birds for a long time and are generally enthusiastic about conservation measures to help protect populations.
The black stilt, which is restricted to New Zealand, is considered Critically Endangered, facing an extremely high risk of extinction. It has suffered primarily from habitat destruction and non-native predators introduced by humans, which eat large numbers of black stilt eggs. There are currently fewer than 100 black stilts in existence. The Hawaiian subspecies of the black-winged stilt is also considered Endangered, facing a very high risk of extinction. There are approximately 1,800 individuals left in the wild. Populations have declined due to habitat destruction and predators introduced by humans.
Physical characteristics: The black-winged stilt has long pink legs and a straight or upwardly curved black bill. In the male, the back and wings are black, the belly is white, and the tail is marked with gray bands. Females have dullish brown backs. The color of the head and neck varies in black-winged stilts from white to black.
Geographic range: The black-winged stilt is widely distributed and occurs on all continents except Antarctica.
Habitat: Black-winged stilts occupy wetland habitats including marshes, swamps, lakeshores, river-edges, and flooded fields.
Diet: Black-winged stilts eat aquatic insects, mollusks, crustaceans, worms, small fish, and tadpoles. They sometimes forage, or search for food, at night, particularly when there is no moon and therefore little light.
Behavior and reproduction: Black-winged stilts can be found in large flocks of as many as several thousand individuals. They have a display where they leap up and then float down, but it is not known what the purpose of the display is. Their call is described as a sharp "yep" sound.
Black-winged stilts and people: No significant interactions between black-winged stilts and people are known.
Conservation status: The black-winged stilt is not considered threatened globally, but the Hawaiian subspecies is considered Endangered. There are about 1,800 individuals left in the wild. ∎
Physical characteristics: American avocets have blue legs and upwardly curved black bills. The wings and the back are black. The head, neck, and breast are gray during the nonbreeding season but change to orange during the breeding season. Males and females are similar in color but males are often larger. Females have shorter bills with a more pronounced upward curve.
Habitat: American avocets use temporary wetland areas, such as areas that flood for part of the year, in the western United States, as well as more permanent wetland habitats.
Diet: American avocets eat aquatic insects, crustaceans, worms, and small fish. They also eat seeds. American avocets often forage, or look for food, in large flocks. They swing their bills through the water to find food, but are also known to peck at food or plunge underwater for it.
Behavior and reproduction: American avocets are found in large flocks during the nonbreeding season. During the breeding season, male-female breeding pairs form and defend territories from other individuals. American avocets threaten an intruder by facing the other bird and extending their necks. Females generally lay four eggs at a time in a grass-lined nest on the ground. Eggs hatch after twenty-two to twenty-nine days. Both the male and female help incubate, or sit on, the eggs, and both feed the chicks once they hatch. Chicks leave the nest after four or five weeks.
American avocets and people: The American avocet was hunted in its habitats in California during the early 1900s, but this practice has stopped.
Conservation status: The American avocet is not considered threatened at this time. However, pollution and destruction of wetland habitats have led to population declines in many parts of its range. ∎
FOR MORE INFORMATION
del Hoyo, J., A. Elliott, and J. Sargatal, eds. Handbook of the Birds of the World. Vol. 3, Hoatzin to Auks. Barcelona: Lynx Edicions, 1996.
Perrins, Christopher, ed. Firefly Encyclopedia of Birds. Buffalo, NY: Firefly Books, 2003.
"Avocets, Stilts." Bird Families of the World, Cornell University. http://www.es.cornell.edu/winkler/botw/recurvirostridae.html (accessed on May 1, 2004).
"Family Recurvirostridae (Avocets and Stilts)." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/classification/Recurvirostridae.html#Recurvirostridae (accessed on May 1, 2004).
"Recurvirostridae (Stilts and Avocets)." The Internet Bird Collection. http://www.hbw.com/ibc/phtml/familia.phtml?idFamilia=57 (accessed on May 1, 2004).