Western Snowy Plover

Charadrius alexandrinus nivosus

Description

The western snowy plover, Charadrius alexandrinus nivosus, is a small, pale-colored shorebird that is light above with a dark patch on the crown, sides of the head, and either side of its upper breast. Its underparts and portions of the head are white.

Behavior

The breeding season of coastal populations extends from mid-March through mid-September. Nest initiation and egg laying occurs from mid-March through mid-July. The usual clutch size is three eggs. Both sexes incubate the eggs.

Chicks are precocious, leaving the nest within hours after hatching to search for food. Fledging (reaching flying age) requires an average of 31 days. Broods rarely remain in the nesting territory until fledging occurs. The species will nest again after loss of a clutch or brood. Double brooding and polygamy (where the female successfully hatches more than one brood in a nesting season with different mates) have been observed in coastal California and may also occur in Oregon. After loss of a clutch or brood or successful hatching of a nest, the species may nest again in the same colony site or move, sometimes up to several hundred miles, to new colony sites to nest.

Nest success (percentage of nests hatching at least one egg) ranges from 0 to 80% for coastal species. Instances of low nest success have been attributed to a variety of factors, including predation, human disturbance, and inclement weather conditions. Reproductive success ranges from 0.05 to 2.4 young fledged per female, pair, or nest. In 1986, it was estimated that the species must fledge 0.8 young per female to maintain a stable population. Reproductive success falls far short of this threshold at many nesting sites.

The species breeds in loose colonies with the number of adults at coastal breeding sites ranging from two to 318. The coastal population consists of both resident and migratory birds. Some birds winter in the same areas used for breeding. Others migrate either north or south to wintering areas.

The species forages on invertebrates in the wet sand and among surf-cast kelp within the intertidal zone; in dry, sandy areas above the high tide; on salt pans and spoils sites; and along the edges of salt marshes and salt ponds.

The species is most active during the early morning when it is cool. Afternoons and evenings, when it is hot, are spent resting or roosting.

Habitat

The Pacific coast populations of the species breed primarily on coastal beaches from southern Washington to southern Baja California, Mexico. Nesting habitat is unstable as a result of unconsolidated soil characteristics influenced by high winds, storms, wave action, and colonization by plants. Other less common nesting habitat includes salt pans, coastal-dredged spoil disposal sites, dry salt ponds, and salt pond levees. Sand spits, dune-backed beaches, non-vegetated beach strands, open areas around estuaries, and beaches at river mouths are the preferred coastal habitats for nesting. The species winters primarily in coastal California and Mexico.

Nest sites occur in flat, open areas with sandy or saline substrates; vegetation and driftwood are usually sparse or absent. The majority of individuals are site-faithful, returning to the same breeding site in subsequent breeding seasons.

Distribution

Historic records indicate that nesting individuals were once more widely distributed in coastal California, Oregon, and Washington than they were at the end of the twentieth century. In coastal California, the species bred at 53 locations prior to 1970. Since that time, no evidence of breeding birds has been found at 33 of these 53 sites, representing a 62% decline in breeding sites. The greatest losses of breeding habitat were in southern California, within the central portion of the coastal breeding range. In Oregon, the species historically nested at 29 locations on the coast. In 1990, only six nesting colonies remained, representing a 79% decline in active breeding sites. In Washington, the species formerly nested in at least five sites on the coast. By 2000, only two colony sites remain active, representing, at minimum, a 60% decline in breeding sites.

In addition to loss of nesting sites, the breeding population in California, Oregon, and Washington declined 17% between 1977 and 1989. Declines in the breeding population have been specifically documented in Oregon and California. Breeding season surveys of the Oregon coast from 1978 to 1992 show that the number of adults declined significantly at an average annual rate of about 5%. The number of adults declined from a high of 139 in 1981 to a low of 30 in 1992. In 1981 the coastal California breeding population was estimated to be 1,565 adults, an 11% decline.

Although there are no historic data for Washington, it is doubtful that the species' breeding population was ever very large in this state. Nevertheless, loss of nesting sites probably has resulted in a reduction in overall population size. In the late twentieth century, less than 30 birds nested on the southern coast of Washington. In 1991, there was only one successful brood detected in the state. Survey data also indicated a decline in wintering individuals, particularly in southern California. The number of individuals observed during Christmas bird counts from 1962 to 1984 significantly decreased in southern California despite an increase in observer participation in the counts. This observed decline was not accompanied by a significant loss of wintering habitat over the same period.

As of the late 1990s, this species was distributed along the Pacific coast from southern Washington to southern Baja California, Mexico, Colorado, Kansas, Oklahoma, and north-central Texas, as well as coastal areas of extreme southern Texas, and possibly extreme northeastern Mexico. Although previously observed only as a migrant in Arizona, small numbers have bred there in recent years. The species occurs on federal, state, and privately owned land throughout its range. The species occupied a similar, more extensive range in the past over the same general areas. The U. S. Fish and Wildlife Service lists the species as threatened in California, Oregon, and Washington, as well as the Pacific coast population in Baja California, Mexico.

Threats

The most important form of habitat loss to coastal breeding individuals has been the encroachment of European beachgrass (Ammophila arenaria ). This non-native plant was introduced to the West Coast around 1898 to stabilize dunes. Since then, it has spread up and down the coast and now is found from British Columbia to southern California (Ventura County). In the late twentieth century, European beachgrass was a major dune plant occurring at about 50% of California breeding sites and all of those in Oregon and Washington. Stabilizing sand dunes with European beachgrass has reduced the amount of nonvegetated area above the tideline, decreased the width of the beach, and increased its slope. These changes have reduced the amount of potential nesting habitat for the species on many beaches and may hamper brood movements. The beachgrass community also provides habitat for predators of the species which historically would have been largely precluded by the lack of cover in the dune community. In addition, the presence of beachgrass may adversely affect food supplies. The abundance and diversity of sand dune arthropods are markedly depressed in areas dominated by European beachgrass.

Urban development has also contributed significantly to the loss of breeding sites. The construction of residential and industrial developments, and recreational facilities—including the placement of access roads, parking lots, summer homes, and supportive services—have permanently eliminated valuable nesting habitat on beaches in southern Washington, Oregon, and California. The species' use of human-made habitat, such as salt evaporators and dredged spoil sites, apparently has not compensated for the loss or degradation of habitat in other areas.

Sand mining operations at numerous locations in California also may be eliminating potential habitat by interrupting buildup of the sand profile. Stabilization efforts also may interrupt this process, resulting in beach erosion and loss of nesting habitat.

In the habitat remaining for nesting, human activity (e.g., walking, jogging, running, pets, horseback riding, off-road vehicle use, and beach raking) is a key factor in the ongoing decline in this species' breeding sites and the breeding populations in California, Oregon, and Washington. In all of Los Angeles County and parts of Orange County, California, entire beaches are raked on a daily to weekly basis to remove trash and tidal debris. Even if human activity was low on these beaches, grooming activities completely preclude the possibility of successful nesting attempts. Food availability on raked beaches also may be depressed for both breeding and wintering populations, because surf-cast kelp and associated invertebrates are removed and the upper centimeter of sand substrate is disturbed.

Eggs, chicks, and adults of this species are taken by a variety of avian and mammalian predators. These losses, particularly to avian predators, are exacerbated by human disturbances. Of the many predators, American crows, ravens, and red fox have had a significantly adverse effect on reproductive success at several colony sites. Because crows and ravens, in particular, thrive in urban and agricultural areas, late twentieth century coastal populations of these species were probably greater than historic populations. Accumulations of trash at beaches attracts these as well as other predators, including striped skunks, gulls, and raccoons. At nesting sites on the Oregon coast, nest losses of up to 68% have been attributed to crows and ravens.

Conservation and Recovery

On most federal land containing active breeding sites, few measures have been implemented specifically for this species. Most nesting areas on federal land, with the exception of military bases, have unrestricted human access all year. In Oregon, the U.S. Army Corps of Engineers is proposing two projects to create or improve nesting habitat using dredged spoils. Access improvements for recreational purposes are ongoing at several beaches on federal land.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 1306
Albuquerque, New Mexico 87103-1306
Telephone: (505) 248-6911
Fax: (505) 248-6915
http://southwest.fws.gov/

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 25486
Denver Federal Center
Denver, Colorado 80225
http://www.r6.fws.gov/

Reference

U. S. Fish and Wildlife Service. March 5, 1993. "Determination of Threatened Status for the Pacific Coast Population of the Western Snowy Plover." Federal Register 58 (42): 12864-12874.