Snowy plover

Two subspecies are commonly recognised:[11][6]

• Charadrius nivosus nivosus (Cassin, 1858): The nominate subspecies, found in western North America and the Gulf of Mexico. This subspecies includes Charadrius nivosus tenuirostris, the Cuban snowy plover.[11][12]

• Charadrius nivosus occidentalis (Cabanis, 1872): Found on the Pacific coast of South America. It is slightly larger than the nominate subspecies, the lore (the area between eye and beak) is white, and the black patch on the forehead is slightly broader.[11]

The typical call is a sweet, repeated "tu-wheet", which is given in a wide range of contexts.[11][13] In males, these include, amongst others, 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 give a "peep" call from up to two days before hatching and continuing until their first flight.[11]

The species feeds on invertebrates such as crustaceans, worms, beetles, and flies. An analysis of feces from a coastal population of California during breeding season revealed 72% beetles, 44% flies, and 25% insect larvae. Prey is taken from above and below the sand surface, from plants or carcasses. In inland habitats, snowy plovers usually forage on wet substrates that may be under a shallow water cover.[11] As is typical for plovers, prey is found visually by briefly standing to scan the area, which is followed by running and capturing.[11][13] Snowy plovers also forage by probing the substrate with their bills, by charging or hopping into accumulations of flies, and by "foot trembling" on wet substrates or in shallow water, where one foot shakes to stirr up prey. Brine fly larvae are often shaked before consumption, and captured flies are often bitten two or three times times. Snowy plovers may forage during day and night, with one invividual observed feeding in almost complete darkness. Snowy plovers drink when fresh water is available, but when it is not, they can sustain on the water content of their prey.[11]

At the beginning of the breeding season, the male, while still unpaired, will establish and defend an territory, which is then advertised to a female by calling and excavating scrapes. A pair will continue to defend the territory. After the chicks hatch, the brood will soon then begin to move around, when the adults will defend the surrounding radius rather than a fixed territory. When defending a territory, males may attempt to intimidate conspecifics by using the "Upright Display" posture, in which the body is upright with erected breast feathers. They may also run or fly at, or fight with intruders. Fighting may involve jumping at each other breast-to-breast with flapping wings and mutual pecking and shoving. In some cases, combatans pull on each others feathers, and may even pull out a flight feather. Fights with intermittent short breaks can last up to 1.5 hours. Territories are defended not only against conspecifics but also against some other bird species, including semipalmated plovers and whimbrels. Territories are probably not important for protecting food resources, as the plovers often feed in flocks up to 6 km away from their territories. However, in Kansas and Oklahoma, where the birds are more stationary, protection of feeding grounds could be more important. The size of territories is variable, and sizes between 0.1 and 1 ha have been reported.[11]

Outside the breeding season, snowy plovers will often roost in groups of several to more than 300 birds. Roosting places are typically on the ground in footprints, vehicle tracks, or behind objects such as driftwood. When attacked by a bird of prey, the birds will take flight to form a highly coordinated flight formation.[11]

Three eggs in a nest on a beach in San Diego County, California

Snowy plovers are facultative polygamous, with females, and less frequently males, often abandoning their mate soon after the chicks have hatched. The deserting female will then pair with a new male and renest, sometimes a few hundred kilometers away from its first brood, while the male will continue to rear the chicks. This polygamy is most pronounced where the breading 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 favour 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.[11] The polygamous mating system of the snowy plover is uncommon, but the closely related Kentish plover shows a similar behavior.[3]

Snowy plovers nest in ground 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 choosen.[11]

The species lies 3 eggs on average, but clutch size ranges from 2 to 6 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 31 mm in length, 23 mm in width, and 8.5 g 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 spent only around a fourth of daytime incubating. In coastal areas of California, females tend to inclubate 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, amongst others. Under hot conditions greater 40°C, the male and female take turns every hour or less to prevent overheating.[11]

A day before hatching, chicks and parents communicate by calling. After hatching, the parents will carry eggshells away from the nest. The chicks are presocial 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 58% of the time on average. When parents sense potential danger such as approaching predators, the chicks will lie flat against the ground. In western North America, chicks are attended for 29 to 47 days after hatching, often by the male after the female deserted. In the more eastern populations, however, chicks are often attended until they fledge.[11]

The University of California, Santa Barbara (UCSB) is currently endeavoring to rehabilitate snowy plover populations by protecting beaches along the central California coastline that runs along part of the university campus.[19] UCSB has had some success in encouraging reproduction; the university also often trains students and other volunteers to watch over protected beaches during the daytime to ensure no one disturbs nesting grounds. But even with the conservation efforts, their population is slowly dwindling, it's estimated that only about 2,500 western snowy plovers breed along the Pacific Coast.[20]

Scientists from Point Blue Conservation Science and the National Park Service (NPS) have instituted management measures to encourage successful snowy plover reproduction efforts on Point Reyes National Seashore. Vulnerable nests are protected by exclosures, fencing enforces seasonal closures around nesting habitat, and sections of the Great Beach are closed to reduce human disturbance.[21] To counteract the impact of increased recreation on weekends and holidays, the park uses informational signs and brochures detailing the vulnerability of the species, while volunteer docents have been present to help educate visitors on the species since 2001.[22]

The beaches lining Vandenberg Space Force Base on the Central coast of California are also home to several protected areas where breeding has been successful in recent years. Access to these beaches is limited to certain times of the year, and very specific areas are open to keep the bird protected. Most of these beaches are only open to military personnel and their families.[23]

Conservation of the western snowy plover is being done by a consortium of organizations including the U.S. Fish and Wildlife Service, the U.S. Forest Service, the Bureau of Land Management, the Oregon Department of Fish and Wildlife, and the Oregon Parks and Recreation Department. Since conservation measures were put in place in the 2000s, including beach restrictions and control of invasive beach grasses, snowy plover populations have increased by a factor of more than seven.[24]