Snowy plover

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. Before the transfer, Anarhynchus contained only one species, the wrybill from New Zealand. 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. • Anarhynchus nivosus occidentalis (Cabanis, 1872): Found on the Pacific coast of South America. It is slightly larger than the nominate subspecies, the (the area between eye and beak) is white, and the black patch on the forehead is slightly broader. A 2020 study suggested that the snowy plover populations can be subdivided into four distinct demes (groups of individuals more genetically similar to each other than to other individuals): The western nivosus deme in western North America, the eastern nivosus deme in Florida, the tenuirostris deme on the Caribbean islands and Bermuda, and the occidentalis deme in South America. The study found little genetic exchange between these demes, except for a strong migration from the western to the eastern nivosus deme (but not vice versa). ==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. 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. ==Behavior and ecology==

Feeding The species feeds on invertebrates such as crustaceans, worms, beetles, and flies. An analysis of feces from a coastal population in California during breeding season found beetles in 72%, flies in 44%, and insect larvae in 25% of the feces. Prey is taken from above and below the sand surface, from plants, and from carcasses. In inland habitats, snowy plovers usually forage on wet substrates that may be under a shallow water cover. Polygamy is most pronounced where the breeding season is long, when birds may start two, and sometimes three, broods per season. On the other hand, birds do generally not brood twice in the Great Plains, where the breeding season is short. A biased sex ratio also appears to favor polygamy: males are generally more common than females, with one study reporting that males were 1.4 times more common than females in California. The causes for such pronounced sex ratios are unknown. Rarely, males breed with two females at the same time. Pairs can also be reestablished in the next breeding season, which occurred in 32 to 45% of cases in central California, or within the same season in the third breeding attempt of the female. The polygamous mating system of the snowy plover is uncommon in birds, but the closely related Kentish plover shows a similar behavior. Snowy plovers nest in nest scrapes that are excavated by the male as an important part of the courtship ritual. In the coastal areas of California, males excavated an average of 5.6 scrapes per territory. A scrape may be constructed within a few minutes, often near conspicuous landmarks such as rocks and grass patches. One of these scrapes is later selected by the pair for nesting, commonly the scrape where most copulations took place. Both before and during incubation, the adults continue to line the nest with small objects such as stones and shell pieces. Where the ground is too hard to construct scrapes, other depressions such as animal and vehicle tracks are chosen. The species lays three eggs on average, but clutch size ranges from two to six eggs. When only a single egg is produced, the clutch is usually abandoned. Eggs are oval or asymmetric in shape and have a matte and smooth surface. In coastal California, they average at in length, in width, and in weight, which accounts for 20% of the body weight of the female. Egg color is brownish-yellow, with dark brown or black speckles that become more numerous towards the blunt end of the egg. The female lays one egg every 47 to 118 hours until the clutch is complete. The time interval between egg laying and hatching varies geographically and seasonally, ranging between 23 and 49 days. Continuous incubation starts upon clutch completion; while still incomplete, males and females spend only about a quarter of the daytime incubating. In coastal areas of California, females tend to incubate during the day, while males incubate at night. The reason for this pattern is unclear, and hypotheses include a need of the female to feed at night to regain energy lost from egg laying and the need of the male to defend the territory during daytime. Under hot conditions greater , the male and female take turns at least once per hour. A day before hatching, chicks and parents begin to communicate by calling. After hatching, the parents will carry eggshells away from the nest. The chicks are precocial and able to walk and swim one to three hours after hatching. Parents do not feed their chicks, but will lead them to feeding areas. Parents will continue to brood their chicks after hatching – in the coastal areas of northern California, chicks less than 10 days old were brooded for an average of 58% of each day. In western North America, chicks are looked after for 29 to 47 days after hatching, often by the male after the female has deserted. In the more eastern populations, however, chicks are often cared for until they fledge. Predators and mortality Adults are preyed upon by birds of prey and various mammals including feral cats and foxes, with a wider range of predators preying on chicks and eggs. Adults will usually run away from an approaching predator or human, but may also take flight. Approaching birds of prey cause adults to duck on their nests, while roosting flocks will take flight to form a highly coordinated flight formation in which they move back and forth. Parents will signal their chicks to lie flat against the ground when sensing potential danger. They may then attempt to distract predators from their chicks by calling and flying around. Parents also use injury feigning, when they will run away and move their wings as if they are broken, or lie on the ground while crouching or flapping. Common diseases include botulism, and common parasites include bird lice. The average life span has been estimated at 2.7 years, and the oldest snowy plover on record was at least 15 years old. == Status and conservation ==

in California The snowy plover is among the rarest endemic shorebirds in the Americas. On US beaches, disturbance by humans and dogs is another significant cause for the abandonment of areas. One 2001 study found that at a public beach at Coal Oil Point, each plover was disturbed every 27 minutes on average during weekends and every 43 minutes during the week. The study further found that the plovers have been more sensitive to dogs than to humans, and that most disturbances occurred when the plovers were approached by less than . A 2003 study of two beaches at Point Reyes National Seashore found that chick mortality was 69% greater on weekends compared to weekdays in 1999 and 72% greater in 2000, demonstrating the negative effects of human recreation. Nests have also been directly crushed by vehicles, walking humans, and, in inland populations, by cattle. Several additional threats have been documented. Predation on chicks and eggs by crows, ravens, skunks, and invasive red foxes has intensified in some areas. Crows and ravens may be attracted to plover breeding areas by human food sources. Conservation measures , California In 1993, the Pacific coast population of the US was listed as a "threatened" under the Endangered Species Act of 1973, and a recovery plan followed in 2007. The plan focuses on three main conservation measures: closure of upper beach areas to the public during breeding season; protection against predators; and habitat restoration. Closure of beach areas was most effective when including fencing against dogs and a 30 m buffer zone. Egg predators were controlled by both fencing individual nests and predator removal. Habitat restoration focused on the removal of the invasive European beachgrass. Measures are also in place to protect some other snowy plover habitats elsewhere in the US. In the Great Salt Plains in Oklahoma, dams and fences were erected around nesting areas to prevent flooding and predation, but proved ineffective. ==References==