Nombre en español: Caracolero Común

Nombre cientifico: Rostrhamus sociabilis

Nombre en ingles: Snail Kite

Familia: Accipitridae

Foto: Mauricio Ossa/Daniel Orozco

El caracolero común (Rostrhamus sociabilis), también conocido como elanio caracolero, gavilán caracolero o milano caracolero, es una especie de ave accipitriforme de la familia Accipitridae que cría de manera residente en América del Sur tropical, las Antillas y el centro y sur de Florida.

Características

Las alas son largas, anchas y redondeadas. La cola es larga; el obispillo y las coberteras infracaudales son blancos. El pico, oscuro y muy ganchudo, es una adaptación a su dieta, que consiste casi exclusivamente en caracoles de laguna del género Pomacea (familia Ampullariidae). El macho adulto tiene el plumaje gris azulado oscuro, con las remeras más oscuras; las patas y la cera son rojas. La hembra adulta tiene el dorso castaño oscuro y el vientre pálido con muchas franjas; la cara es blanquecina con zonas más oscuras detrás y sobre el ojo; las patas y la cera son de color amarillo o naranja. Los inmaduros son similares a la hembra adulta, pero la corona presenta franjas.

Historia natural

Es un ave de humedales de agua dulce, que anida en arbustos o en el suelo. Pone de 3 a 4 huevos. Mide unos 45 cm de longitud y 120 cm de envergadura. Es una especie gregaria; forma grandes bandadas en invierno. El vuelo es lento, con la cabeza hacia abajo en busca de caracoles. Una vez localizado el caracol, lo captura y va a su rama favorita a comérselo.Con una pata se sujeta en la rama y en la otra sostiene al caracol. Mientras lo sostiene con la garra, con el pico hace un agujero en la concha, en la parte más inicial de la espira donde el caracol está retraído y por él lo extrae sin comerse el opérculo. Uno encuentra esparcidos por la orilla del río Paraná las conchas agujereadas y los opérculos, en montones.

El caracolero común es una especie en peligro en los Everglades de Florida, con una población de menos de 400 parejas de cría. Se ha demostrado que el control del nivel del agua en los Everglades está diezmando la población de caracoles.

Subespecies

Se reconocen tres subespecies de Rostrhamus sociabilis:

Rostrhamus sociabilis plumbeus – marismas de agua dulce de Florida, Cuba e Isla de la Juventud.
Rostrhamus sociabilis major – este de México y norte de Guatemala (Petén).
Rostrhamus sociabilis sociabilis – de Honduras y Nicaragua a Brasil y noreste de Argentina.

Snail kite

The snail kite (Rostrhamus sociabilis) is a bird of prey within the family Accipitridae, which also includes the eagles, hawks, and Old World vultures. Its relative, the slender-billed kite, is now again placed in Helicolestes, making the genus Rostrhamus monotypic. Usually, it is placed in the milvine kites, but the validity of that group is under investigation.

Description

Snail kites are 36 to 48 cm (14 to 19 in) long with a 99–120 cm (39–47 in) wingspan. They weigh from 300 to 570 g (11 to 20 oz). There is very limited sexual dimorphism, with the female averaging only 3% larger than the male. They have long, broad, and rounded wings, which measure 29–33 cm (11–13 in) each. Its tail is long, at 16–21 cm (6.3–8.3 in), with a white rump and undertail coverts. The dark, deeply hooked beak, measuring 2.9–4 cm (1.1–1.6 in) is an adaptation to its diet. The tarsus is relatively long as well, measuring 3.6–5.7 cm (1.4–2.2 in).

The adult male has dark blue-gray plumage with darker flight feathers. The legs and cere are red. The adult female has dark brown upperparts and heavily streaked pale underparts. She has a whitish face with darker areas behind and above the eye. The legs and cere are yellow or orange. The immature is similar to adult female, but the crown is streaked.

It flies slowly with its head facing downwards, looking for its main food, the large apple snails. For this reason, it is considered a molluscivore.

Taxonomy

Lerner and Mindell (2005) found R. sociabilis sister to Geranospiza caerulescens, and that those two along with Ictinea plumbea were basal to both the buteogallus and buteo clades. They concluded that Rostrhamus belonged in Buteoninae (sensu stricto) and not in Milvinae, but noted that more investigation was needed.

Distribution and ecology

The snail kite breeds in tropical South America, the Caribbean, and central and southern Florida in the United States. It is resident all-year in most of its range, but the southernmost population migrates north in winter and the Caribbean birds disperse widely outside the breeding season.

It nests in a bush or on the ground, laying 3–4 eggs.

The snail kite is a locally endangered species in the Florida Everglades, with a population of less than 400 breeding pairs. Research has demonstrated that water-level control in the Everglades is depleting the population of apple snails. However, this species is not generally threatened over its extensive range.

In fact, it might be locally increasing in numbers, such as in Central America. In El Salvador, it was first recorded in 1996. Since then, it has been regularly sighted, including immature birds, suggesting a resident breeding population might already exist in that country. On the other hand, most records are outside the breeding season, more indicative of post-breeding dispersal. In El Salvador, the species can be observed during the winter months at Embalse Cerrón Grande, Laguna El Jocotal, and especially Lago de Güija. Pomacea flagellata apple snails were propagated in El Salvador between 1982 and 1986 as food for fish stocks, and it seems that the widespread presence of high numbers of these snails has not gone unnoticed by the snail kite.

This is a gregarious bird of freshwater wetlands, forming large winter roosts. Its diet consists almost exclusively of apple snails.

Snail kites have been observed eating other prey items in Florida, including crayfish in the genus Procambarus and black crappie. It is believed that snail kites turn to these alternatives only when apple snails become scarce, such as during drought, but further study is needed. On 14 May 2007, a birdwatcher photographed a snail kite feeding at a red swamp crayfish farm in Clarendon County, South Carolina.