Snowy plover
The snowy plover is a small shorebird found in the Americas. It is a member of the bird family Charadriidae, which includes the plovers, dotterels, and lapwings. The snowy plover was originally described by John Cassin in 1858, but was classified as a subspecies of the Kentish plover in 1922. Since 2011, the snowy plover has been recognized as a distinct species based on genetic and anatomical differences from the Kentish plover. Two or three subspecies are recognized, distributed along the Pacific coast of North America, Ecuador, Peru, and Chile, in several inland areas of the US and Mexico, along the Gulf Coast, and on Caribbean islands. The coastal populations consist of both residential and migratory birds, whereas the inland populations are mostly migratory. It is one of the best studied endemic shorebirds of the Americas, and one of the rarest.
Snowy plovers are pale brown above and white below, with a white band on the hind neck. During the breeding season, males have black patches behind the eye and on the side of the neck; the neck patches are separated from each other and do not form a continuous breast band as in many other plovers. Snowy plovers can also be distinguished from other plovers in having an all-black and slender bill, and gray to black legs. The typical call is a repeated "tu-wheet".
This plover inhabits open areas in which vegetation is absent or sparse, in particular coastal sand beaches and shores of salt or soda lakes, where it feeds on invertebrates such as crustaceans, worms, beetles, and flies. At the beginning of the breeding season, males excavate multiple nest scrapes that are advertised to females; one of these scrapes is later selected for breeding. Some females will desert their brood soon after the chicks hatch to re-mate with another male, while their first mate will continue to rear the chicks. Such polygamy is uncommon in birds, and is possibly a strategy to maximize breeding success. There are more males than females – 1.4 times as many in California – and the more pronounced this sex ratio imbalance is, the more females engage in polyandrous behavior.
The snowy plover is listed as near threatened by the International Union for Conservation of Nature. The main threats are habitat destruction due to invasive beach grasses, urban development, as well as frequent disturbance due to recreational uses of beaches. Conservation measures on the US Pacific coast include roping-off beach areas that are used for breeding, the removal of invasive beach grasses, and protection against egg predators. While such measures have been successful locally, the global population is thought to be in decline.
Taxonomy and systematics
The snowy plover was first described by John Cassin in 1858 as Aegialitis nivosa, based on a skin collected in 1854 by William P. Trowbridge in Presidio, which later became part of San Francisco. This skin, the holotype of the species, was subsequently lost. Although originally part of the collection of the National Museum of Natural History, it was given to the collector Henry E. Dresser of England in 1872. In 1898, the Dresser collection was transferred to the Victoria University of Manchester, but the skin was apparently not part of this transfer. Joseph Grinnell, who attempted to locate the holotype in 1931, suggested that Dresser may have been unaware of the specimen's significance and may have given it elsewhere. The snowy plover is one of the best-studied endemic shorebirds of the Americas, although most of this research was carried out on western North American populations, with few monitoring programs targeting the South American and eastern North American populations.Plovers are a subfamily of small shorebirds that breed in open habitats on all continents except Antarctica. Together with the lapwings, they form the family Charadriidae. The snowy plover was traditionally considered to be a species within the genus Charadrius, which comprised 32 extant species and was therefore the most species-rich genus of the family. However, a 2013 genetic analysis found that the lapwings are nested within Charadrius; the latter is therefore polyphyletic. Some subsequent studies confirmed this and proposed to split Charadrius into five separate genera. The snowy plover, formerly Charadrius nivosus, was transferred into the genus Anarhynchus, as Anarhynchus nivosus, along with 22 other plover species; in 2023, this transfer was recognized by the International Ornithologists' Union. Before the transfer, Anarhynchus contained only one species, the wrybill from New Zealand. The name Anarhynchus derives from the Ancient Greek ἀνα- meaning and ῥυγχος meaning. The species name nivosus is Latin for.
The snowy plover appears to be most closely related to the Kentish, the white fronted, the Malaysian, the chestnut-banded, and the red-capped plover, as shown in a cladogram from a 2015 study:
The snowy plover is closely related, and visually similar, to the Kentish plover of Eurasia and Africa. Harry C. Oberholser, in 1922, argued that the differences in plumage between these species are not consistent, and no clear line of demarcation could be drawn. Consequently, he classified the two subspecies of the snowy plover that were recognized at that time as subspecies of the Kentish plover. This assessment was subsequently followed by most authors, until a 2009 genetic study re-established the snowy plover as a separate species. This study noted that, besides differences in the mitochondrial and nuclear DNA, snowy plovers differ from Kentish plovers in being smaller, having shorter and wings, different chick plumages, and different advertisement calls of the males. In 2011, the International Ornithological Congress and the American Ornithologists' Union recognized them as separate species.
Subspecies
Two to three subspecies are commonly recognized:- Anarhynchus nivosus nivosus : The nominate subspecies, found in North America west of Louisiana.
- Anarhynchus nivosus tenuirostris : The Cuban snowy plover, found in North America east of Louisiana. The distinction of this subspecies from the nivosus subspecies is contested, but two genetic analyses in 2007 and 2020 have supported its separation.
- Anarhynchus nivosus occidentalis : Found on the Pacific coast of South America. It is slightly larger than the nominate subspecies, the is white, and the black patch on the forehead is slightly broader.
Description
The snowy plover is a plump shorebird with a large head, a short and slender bill, and short neck and tail. It is a small plover, with adults ranging from in length, from in wingspan, and from in weight. Its body is typically held horizontally. Compared to other plovers, its legs are relatively long and its wings short. The bill is black, the iris dark brown, and the legs gray to black.Snowy plovers are pale brown above and white below, with a white band on the hind neck and a smudgy . Breeding males have black patches behind the eye, on the sides of the neck, and on the forehead. In males, the may be reddish at the start of the breeding season. The breeding female is slightly duller, and typically one or more of the patches are partly or completely brown. The neck patches on each side are well separated and rarely joined at the front, giving the appearance of a "broken" breast band in contrast to the continuous breast band in many other plovers. Outside the breeding season, the neck and ear patches are pale and the forehead patch is absent, and plumages of males and females cannot be distinguished. Newly hatched chicks have pale upper sides with brown to black spots and are white below.
Similar species within its range include the piping plover, the collared plover, the semipalmated plover, and Wilson's plover. Amongst other features, the snowy plover differs from these species in its slender and entirely black bill, in its gray to black legs, and the "broken" breast band.
Vocalizations
The typical call is a repeated "tu-wheet" given in a wide range of contexts. In males, these include advertisement while standing in territories and courtship. In both sexes, the call may be given in situations of threat, aggression, distress, and alarm. This call differs between sexes, being shorter, quieter, and hoarser in the female. Other calls include a repeated "purrt" that is given during breeding season, for example while flying from nest sites or when other plovers intrude their territory. A single "churr" is mostly given by males while defending territory or offspring from other plovers. Outside the breeding season, a repeated "ti" is given when disturbed while resting, and is often followed by flight. Chicks make a "peep" call from up to two days before hatching while still in the egg, and until their first flight.Distribution and habitat
The snowy plover is distributed along the Pacific coast of North and South America, in areas inland of the US and Mexico, along the coast of the Gulf of Mexico, and on the Caribbean islands and Bermuda. On the Pacific coast, it breeds from south Washington down to Oaxaca in Mexico, and non-breeding individuals can be found as far south as Panama. In South America, it breeds from south Ecuador to Chiloé Island in Chile. In the Caribbean, breeding occurs eastwards as far as the Virgin Islands and Margarita Island. The coastal populations consist of both migratory and residential birds; migration occurs over relatively short distances north- or southward along the coast. Inland breeding populations exist in the US eastward to the Great Plains of Kansas and Oklahoma, as well as in Mexico north of Mexico City. These populations are mostly migratory, with western populations migrating to the Pacific coast, and the Great Plains populations to the Gulf of Mexico coast. Breeding has been recorded at elevations up to.The species inhabits open areas in which vegetation is absent or sparse, in particular coastal sand beaches and shores of salt or soda lakes. It also breeds on river bars that are located close to the coast, and adopts human-made habitats such as wastewater and salt evaporation ponds, dammed lakes, and dredge spoils. It requires the proximity of water, although it may breed on salt flats where only very little water remains.