Nombre en español: Avoceta Americano
Nombre en ingles: American Avocet
Nombre científico: Recurvirostra americana
Foto: Francisco Piedrahita
La avoceta americana (Recurvirostra americana) es una especie de ave caradriforme de la familia Recurvirostridae. No se reconocen subespecies. Como todos los miembros de su género, presenta el pico encorvado hacia arriba.
Sus hábitats de cría son pantanos, estanques de pradera, y lagunas o lagos poco profundos en el medio-oeste y en la costa del Pacífico de América del Norte. Anida en la tierra abierta, a menudo en grupos pequeños, a veces con otras aves zancudas.
Son aves migratorias y la mayor parte del invierno lo pasan en las costas pacífica y atlántica del sur de México y los Estados Unidos.
Estos pájaros encuentran su alimento en el agua poco profunda o en el barro o lodo. Comen principalmente crustáceos e insectos.
The American avocet (Recurvirostra americana) is a large wader in the avocet and stilt family, Recurvirostridae. This avocet spends much of its time foraging in shallow water or on mud flats, often sweeping its bill from side to side in water as it seeks its crustacean and insect prey.
Taxonomy and systematics
The American avocet is a bird in the Charadriiformes Order, which includes shore birds, gulls, alcids, plovers, oystercatchers, and auks. Its Family – Recurvirostridae – includes stilts and avocets. The American avocet is one of four avocet species; the Andean avocet, the Pied avocet, and the Red-necked avocet are the remaining three species in the genus.
The American avocet measures 40–51 cm (16–20 in) in length, has a wingspan of 68–76 cm (27–30 in) and weighs 275–420 g (9.7–14.8 oz) The bill is black, pointed, and curved slightly upwards towards the tip. It is long, surpassing twice the length of the avocet’s small, rounded head. Like many waders, the avocet has long, slender legs and slightly webbed feet. The legs are a pastel grey-blue, giving it its colloquial name, blue shanks. The plumage is black and white on the back, with white on the underbelly. During the breeding season, the plumage is brassy orange on the head and neck, continuing somewhat down to the breast. After the breeding season, these bright feathers are swapped out for white and grey ones. The avocet commonly preens its feathers – this is considered to be a comfort movement.
Distribution and habitat
American avocets were previously found across most of the United States until extirpated from the East Coast. The breeding habitat consists of marshes, beaches, prairie ponds, and shallow lakes in the mid-west, as far north as southern Canada. These breeding grounds are largely in areas just east of the rocky mountains including parts of Alberta, Saskatchewan, Montana, Idaho, Washington, Utah, North and South Dakota, Nebraska, Colorado, and even down to parts of New Mexico, Oklahoma and Texas. Their migration route lands them in almost every state in the western United States. The avocet’s wintering grounds are mainly coastal. Along the Atlantic Ocean, they are found in North and South Carolina, Georgia and Florida. There are also wintering grounds along the Gulf of Mexico in Florida, Texas, and Mexico, and along the Pacific Ocean in California and Mexico. There are resident populations in the Mexican States of Zacatecas, San Luis Potosi, Guanajuato, Hidalgo, Mexico City and Puebla, and in Central California.
Behaviour and ecology
The American avocet call has been described as both a shrill and melodic alarm bweet, which rises in inflection over time.
American avocets breed in anything from freshwater to hypersaline wetlands in the western and mid-west United States. American avocets form breeding colonies numbering in dozens of pairs. Throughout the breeding season, birds pair off in a series of copulatory displays. After breeding, the birds gather in large flocks, sometimes amounting to hundreds of birds. Nesting takes place near water, usually on small islands or mucky shorelines where access by predators is difficult. Together, the male and female build a saucer-shaped nest, take turns incubating the four eggs, and tending to the precocial young. Upon hatching, the chicks feed themselves; they are never fed by their parents.
Food and feeding
Avocets tend to prefer habitats with fine sediments for foraging. In the winter, these birds feed extensively on brine shrimp. Usually, this entails the avocet pecking while walking or wading on the shore, but it can also swim to expand foraging area. During the breeding season, avocets continue to eat brine shrimp but switch mainly to consuming brine flies. Brine flies and brine fly larvae are so abundant in avocet breeding grounds that they often blacken the surface of any exposed mud. Brine flies sustain the avocet during its breeding season. The avocet employs both visual and tactile methods of feeding. The primary visual feeding method is pecking at flies. However the avocet will also feed by plunging (wherein the head and neck of the bird are submerged), snatching (wherein the bird catches a flying insect), and bill pursuit (wherein the bird repeatedly opens and closes its bill while moving its head along the surface of the water). Methods of tactile feeding include filtering, scraping, and scythe feeding.
Shooting and trapping of American avocets led to population decline until the 1900s. During this time, the species was extirpated from most of the East Coast of the United States. By 1918, Avocets became protected under the Migratory Bird Treaty Act (16 U.S.C. 703-712). Since that time, other threats have emerged. Contaminants and toxins such as DDT, selenium, and methylmercury, have had significant impacts on American avocet breeding success, especially because Avocet chicks are more susceptible to environmental disruptions than adults. The avocet also faces habitat loss. While agricultural and industrial environments have become alternate habitat for the avocet, natural wetlands are decreasing rapidly.
John James Audubon’s depiction of the American avocet in breeding plumage.
In his famous The Birds of America, John James Audubon describes a day of stalking and spying on the avocet. He judiciously noted their foraging, nesting, defensive, and flight behaviors. See his painting to the right.
The American avocet is protected under the Migratory Bird Treaty Act of 1918.