Black-bellied Plover, Pluvialis squatarola
Black-bellied Plover, Pluvialis squatarola, Wintering Non-breeding Adult. Photograph taken with the rocky shoreline of the greater Bahía de los Ángeles area, Baja California, January 2019. Photograph courtesy of George Flicker, Bahía de los Ángeles. Identification courtesy of Mary & George Flicker, Bahía de los Ángeles.
Background and Identification
The Black-bellied Plover, Pluvialis squatarola, is a member of the Charadriidae Family of Plovers and Lapwings, which has sixty-eight members placed in ten genera and is one of four global species of the Pluvialis Genus. Another name for this species is the Grey Plover. The Black-bellied Plover is wary and functions worldwide as a sentinel for mixed-species assemblages of shorebirds providing immediate alarm calls. As the largest and widest-ranging marine plover species, they have served as a model for studies of other shore birds. They have life spans of thirteen years with high survival rates of their juveniles. In Mexico, they are known as Chorlo Gris.
The Black-bellied Plover is a large plover, with a total length of 27 cm (11 inches) to 31 cm 12 inches). Both sexes weigh between 165 g (5.8 oz) and 395 g (13.9 oz). They have a large head, thick neck, and a large thick, short, bill that tapers to a blunt point. Sexual differences are not common in shorebirds, and that is the case with Black-bellied Plovers. The sexes are similar in appearance and size, known as monomorphism. Their wintering plumage is present from September to February when they have brownish gray to dark brown underparts with most feathers fringed with pale gray-brown, pale gray-brown forehead, supercilium, and auricular areas, a white rump and upper tail coverts, underwing coverts that are uniformly gray-brown with white fringes and dark brown primaries and secondaries. At other times of the year, their breast and sides vary from pure white to grayish, variably mottled brown. Their bills are black, their irises are dark brown, and their legs and feet are medium to dark gray and become black in breeding adults. They have long pointed wings that extend past the tail tip. They have relatively short legs and toes with a well-developed web between the base of the outer and middle toes and a smaller one between the middle and inner toes. They have a hallux (a small hind toe) which is unique among the plover species.
Habitat and Geographical Range
In Mexico, the Black-bellied Plover is a coastal bird found foraging over sandy and muddy flats during low tide periods. They have large eyes that allow them to forage nocturnally. Although generally a coastal bird, the Black-bellied Plover also forages successfully in freshwater and upland habitats. They mainly consume bivalves, crustaceans, insects, invertebrates, and polychaetes, and vary by location and substrate. They are subject to heavy predation by Glaucous Gulls, Herring Gulls, and Jaegers but are known to attack intruders in groups. Their nests are subject to raids by Arctic Fox, Falcons, Northern Harriers, and Owls. They roost in large flocks of up to 1,000 individuals on the upper parts of beaches, dunes, pastures, within salt marshes, and in mangrove trees.
The Black-bellied Plover is a long-distance and high-flight speed migratory species that makes annual spring and fall migrations. They summer and breed in the high Arctic and overwinter in both temperate and tropical climates. They breed in a narrow range and wintering in a wide range. Females usually winter farther south than males and juveniles winter farther south than adults. In Mexico, they are found between October and February along the entire Atlantic and Pacific Coasts. Small populations are also found in the interior of the mainland, at elevations up to 3,700 m (12,100 feet), and on Clipperton Island.
Common Misidentifications
The Black-bellied Plover might be confused with the American Golden Plover, Pluvialis dominica. This species lacks a hind toe, is smaller in stature, and lacks black axillaries. The American Golden Plover is the only other Plover found in Mexico during the winter months.
Conservation Status
From a conservation perspective the Black-bellied Plover is currently considered to be of Least Concern with stable, widely distributed populations. They were heavily pursued by hunters during the 19th and 20th centuries but resisted population eradication. Their breeding grounds tend to be far away from human civilization and thus of low risk of habitat alteration. Their wintering grounds, in some areas, have been lost to human coastal developments. They date to the Pleistocene Period, approximately 2,580,000 to 11,700 years ago.