San Lorenzo Shoreline Wildlife


California least tern
(Sterna antillarum browni)

The California least tern is one of the smallest members of its family, averaging only 23 cm (9 in.) in length. Typically, these terns forage in shallow estuaries and lagoons, diving head first into the water after a wide variety of small fish. Once considered abundant, the California least tern has suffered dramatic declines due to human encroachment and destruction of its nesting habitat. Formerly California least terns regularly nested on sandy beaches and mudflats near the ocean. However, human disturbance related to dredging and development projects have drastically reduced tern nesting habitat. The construction of the Pacific Coast Highway in the early 20th century had a significant impact on California least terns, as well as other shorebirds, by directly destroying nesting beaches as well as making these areas more accessible to human encroachment. Today, the construction of housing developments continues to reduce suitable breeding grounds, and many remaining tern populations choose to nest on mudflats away from the ocean and man-made landfill instead. These more terrestrial sites have made the nesting terns and their chicks increasingly vulnerable to predation by the red fox (Vulpes vulpes) as well as dogs, cats and raccoons. In 1988, three Orange County tern populations suffered losses of 75% due to fox predation. In addition, the ternís fishing grounds have also been severely impacted by dredging, development and pollution. (Source: Pacific Biodiversity Institute.)



Western snowy plover
(Charadrius alexandrinus nivosus)

The snowy plover is widespread in the southern United States, Central and South America, Eurasia, Africa, and Australia. In North America it is a resident on the Pacific Coast from southern Washington south to Baja California, and on the Gulf Coast from Mexico to the Florida panhandle. Once numbering in the thousands, it is estimated that only 1200-1600 western snowy plovers survive along the Pacific Coast. Almost 5% of them live on Ocean Beach in San Francisco. The western snowy plover is listed under the Federal Endangered Species Act as a threatened species because of loss of nesting habitat due to human development, invasion of European beach grass and predation by ravens, foxes, domestic dogs and cats.

The snowy plover usually builds nests in barren or sparsely vegetated areas around saline and alkaline lakes, agricultural evaporation ponds, or levees. These birds tend to concentrate around water to feed when they are not courting or incubating. Both the male and the female incubate eggs. They feed on brine flies, beetles, and small crustaceans. Water birds like snowy plover that linger seasonally to feed and raise young in evaporation pond systems are exposed to high concentrations of heavy metals and other potentially toxic chemicals. Most of these birds are very faithful to their breeding territory and seldom forage or drink from distant wetlands.


California clapper rail
(Rallus longirostris obsoletus)

The South San Francisco Bay is the last stronghold of the endangered California clapper rail. This secretive bird is olive-brown with dark brown streaks -- a cinnamon-colored breast and black & white bars on its flanks. It has long legs and stands about 14 to 16.5 inches tall with a wingspread of about 20 inches. It is compact and has a short neck. Using its long curved beak it feeds at low tide on the mud flats, dining on such tasty creatures as fiddler crabs, crayfish, worms and small fish. As a result of the discharge of highly treated effluent into the Bay, the salinity of the water has changed. Consequently, the food supply, on which the clapper rail depends, and the dense pickleweed, in which it nests, is threatened. The population of the clapper rail has been endangered by the gradual destruction of salt marsh habitats along the California coast.


Peregrine falcon
(Falco peregrinus)

An American Peregrine falcon may be the fastest creature alive. While stooping down on its prey, the falcon has been clocked as high as 200 miles per hour. Their prey consists of doves, pigeon, shorebirds and waterfowl. The peregrine falcon population took a nosedive starting in the 1940's due to DDT contamination in the fish. The chemicals passed down the food chain. Due to the contamination, the falcon's eggs had thin shells and the eggs broke during incubation. Although DDT has been outlawed, it can still be found in falcons today.


Salt marsh harvest mouse
(Reithrodontomys raviventris)

The saltmarsh harvest mouse weighs 8 - 14 g (0.3 - 0.5 oz.). It lives in salt marsh characterized by salt marsh herbs, grasses and reeds. Stems and leaves of salt marsh plants are its major food source. Insects and seeds are also eaten occasionally. It is able to drink salt water, one of the few mammals able to do so. Grass nests are constructed by the saltmarsh harvest mouse. The nests are usually above ground in grass, low shrubs, or small trees. This mouse is mainly nocturnal and is active all year long. It apparently is a good swimmer. Except during the breeding season, it appears to be solitary. Very few of these mice live as long as 1 year in the wild. The saltmarsh harvest mouse has only been known from areas north and south of San Francisco Bay, entirely within the narrow belt of wetlands surrounding the Bay. Its range continues to shrink because of habitat loss due to the draining and filling of wetlands for industrial and suburban development.


Red fox
(Vulpes vulpes)

The lowland red fox, an eastern species, was accidentally introduced when it escaped from a fur farm in the Sacramento Valley. Within the last five years the fox has invaded bayshore salt marshes, where it is a predator on shorebirds and rodents.