San Clemente Island Sage Sparrow

Amphispiza belli clementeae

Description

The San Clemente Island sage sparrow, Amphispiza belli clementeae, is gray with black streaks on its sides and a single black spot on its chest; it has dark cheeks, dark streaks on the sides of its throat, and a white line over the eyes. Length averages 7 in (17.8 cm). In 1898, the San Clemente was separated from the mainland races because of its larger body size and bill.

Behavior

The non-migratory San Clemente Island sage sparrow is essentially a ground dweller. It uses the shrub canopy for feeding, protection, roosting, song perches, and nesting. Nests are usually constructed fairly close to the ground in dense foliage. Breeding habits are similar to its mainland relatives. The sage sparrow nests from mid-March through mid-June. Although clutch size averages four eggs in the mainland races, the island subspecies produces only three eggs. Eggs are incubated for 13-14 days; juveniles molt in late summer. Juveniles undergo a post-juvenile molt by late summer when their plumage from adults becomes indistinguishable. Post-breeding adults and juveniles combine to form foraging flocks. On San Clemente Island, these flocks range from three to 25 individuals, and generally remain within their local habitat. The diet of mainland birds consists of a variety of seeds and other plant material as well as invertebrates, and the island species is thought to have similar feeding habits.

Habitat

The San Clemente Island sage sparrow is restricted to moderately dense, dry scrub areas along the west coast of the island. This plant community occurs only at lower elevations on the island, and consequently the sparrow rarely strays further than 100-130 ft (30.5-39.6 m) above sea level. This habitat, a type of maritime desert scrub, supports a mixture of low-growing, dry-season deciduous shrubs, predominantly box thorn, ragwort, and cactus.

Distribution

The San Clemente Island sage sparrow is restricted to San Clemente Island, California, where early 20th-century ornithologists viewed it as a conspicuous element of the island's fauna. A 1976 survey projected the San Clemente Island population to be 112 birds, and the adult-to-juvenile ratio suggested a stable or slightly expanding population. A more recent study (1986) indicated a somewhat larger and stabilized population of 176-213 pre-breeding and 264-296 post-breeding birds.

Threats

Some of the reasons for the decline of the sage sparrow are the same as for the decline of the loggerhead shrike: reduced or unavailable food supply; habitat destruction by pigs, goats, and military activity; and competition with other birds, especially the white-crowned sparrow, house finch, and horned lark. Other problems are unique to the sage sparrow. It appears to be unable to effectively invade and use marginal habitat. Predation by cats, fox, kestrels and other raptors, harriers, and cowbirds may also threaten the sage sparrow.

Conservation and Recovery

Possible reasons for the overall decline of this sparrow are: a reduced food supply; habitat destruction by feral pigs and goats; and competition with other birds, such as the white-crowned sparrow, house finch, or horned lark, which all partially overlap the sage sparrow's range. The sage sparrow appears unable to effectively use marginal habitat. Predation may also be a significant factor, although no direct evidence has been reported. Some possible predators are feral cats, island fox, kestrels, northern harriers, and barn owls. The island is administered by the U.S. Navy, which has developed a management plan to preserve the native wildlife. A program to remove introduced feral cats, goats, and pigs from the island is already underway and will help to reestablish this species. Revegetation of bird habitat will require planting of maritime sage scrub associates on hills and knolls where wind dispersal of seeds is likely.

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
(503) 231-6121
http://pacific.fws.gov/

Natural Resources Office
Staff Civil Engineer (18N)
NAS North Island (Building 3)
San Diego, California 92135-5018

References

Grinnel, J., and A.H. Miller. 1944. "Distribution of the Birds of California." Pacific Coast Avifauna 27.

Johnson, N.K. 1972. "Origin and Differentiation of the Avifauna of the Channel Islands, California." Condor 74: 295-315.

U.S. Fish and Wildlife Service. 1984. "Recovery Plan for the Endangered and Threatened Species of the California Channel Islands." U.S. Fish and Wildlife Service, Portland.