Western Snowy Plover
The Pacific coast population of the western snowy plover was listed as threatened by the U.S. Fish and Wildlife Service on March 5, 1993. The population has declined due to many factors. Recreational and other human disturbance, loss of habitat to urban development, introduction of beachgrass (Ammophila spp.) and other nonnative species, and expanding predator populations have all contributed to a decline in active nesting areas and in the size of the breeding and wintering populations. It is estimated that about 2,000 snowy plovers may breed along the U.S. Pacific coast and that there are 157 current or historical snowy plover breeding or wintering locations along the U.S. Pacific coast. Channel Islands National Park is one of the few locations in southern California that still supports breeding and wintering populations of western snowy plovers. In the 1990s Santa Rosa and San Miguel Islands had both breeding and wintering populations, but numbers have declined precipitously. A few birds also lived on The Nature Conservancy portion of Santa Cruz. On Santa Rosa the birds inhabited about 16 miles of coastline, while on San Miguel they were present on about 10 miles of shoreline. The Skunk Point area on Santa Rosa is an important nesting area and foraging area for juvenile and migrating plovers. Forty to fifty percent of the nests in this area have been found on rocky outcrops in the backdunes, about 490 to 980 feet (150 to 300 meters) from the shoreline.
Nesting snowy plovers are sensitive to disturbance. Activities that are detrimental to nesting birds include walking, jogging, unleashed dogs, and beachraking, among other uses. Recreationists can inadvertently step on eggs and chicks, destroying them. In addition, adults will stay away from a nest while people are present. Birds generally flush from nests when people come within 328 feet (100 meters). Separation of plover adults from their eggs or chicks may result in increasing mortality due to overheating in the sun, cold, blowing sand, or predators such as gulls or ravens. Trash left on a beach also may attract predators. People may cause broods of snowy plovers to run away from favored feeding areas.
To avoid disturbance of the birds, several of the beaches where snowy plovers currently nest are closed to recreational use. Specifically, all of the shoreline of San Miguel is closed to pubic landing or entry with the exception of Culyer Harbor. On Santa Rosa, the back beaches and sand dunes between and including Skunk Point and just north of East Point are closed to hiking from March 1st to September 15th to protect the nesting area for the snowy plover, a federally listed, threatened shorebird. Please remain on the wet sand (below mean high tide) or the road throughout this area. Landing is prohibited year-round at the beaches around Sandy Point.
In the park, population numbers have declined on both Santa Rosa and San Miguel, concurrently with an overall decline in the breeding population in southern California. On Santa Rosa it is estimated that less than 30 breeding pairs were on the island in 2002 (most recent survey), down from 60 pairs in 1993. An estimated 200 birds still winter on the island's beaches. On San Miguel, snowy plovers are sometimes sighted on beaches during the breeding season, but they are no longer known to breed on the island. An unknown number of birds also winter here.
Different factors may be responsible for these declines on the islands. On San Miguel human disturbance of plovers has not been documented, nor have data been collected on the impacts of people on the Cuyler Harbor beach - the only beach visitors are permitted to use and once an important nesting area. It is believed that the decline in the breeding population on San Miguel may be due to a large increase in the number of northern elephant seals and California sea lions that have occupied snowy plover nesting habitat. This increase occurred simultaneously with the western snowy plover decline.
Several factors may be responsible for the decline of western snowy plovers on Santa Rosa. In the past, ranch activities affected the plovers, including cattle and horses trampling nests and flushing birds from nests. Ungulate carcasses may have attracted predators such as ravens. Raven numbers are thought to be unnaturally high on Santa Rosa, which may be resulting in an increase in predation by ravens on plover eggs. Accumulations of trash also may have attracted predators. In the past, visitors, including hikers, surfers, and kayakers, affected the plovers at Skunk Point. But with the beach closures these impacts are happening less frequently on the beaches. High winds and predators are still a frequent cause of nest loss. In the past winds accounted for 28% to 34% of all nest losses, while predators (e.g., ravens, Santa Rosa Island spotted skunks) accounted for another 26% to 44% of losses. Both Santa Rosa and San Miguel have 20-30 knot winds on a regular basis through the plover nesting season, which can cause eggs to be sandblasted or blown out of the nest when the adult steps off the nest. It is also possible that ravens, which eat plover eggs and chicks, live on the island and may be more numerous than thought due to the presence of ungulate carcasses. In addition, increasing numbers of elephant seals hauling out on the south beaches of Santa Rosa could be reducing nesting habitat.
Did You Know?
The endemic island deer mouse is the only native terrestrial mammal common to all the Channel Islands and is larger than mainland deer mice. Densities of deer mice on the islands can be greater than anywhere else in the world. This makes you happy if you're an owl, but not if you're a camper.