San Clemente Island Bell's Sparrow
Artemisiospiza belli clementeae

San Clemente Bell's Sparrow

A. b. clementeae song (J. Bradley ©2007)

The San Clemente Island Bell's sparrow is a threatened subspecies endemic to San Clemente Island (SCI), California. San Clemente is the southernmost of California’s Channel Islands and supports a unique ecosystem as well as serving as an active U.S. Navy training ground. IWS has been contracted by the Navy to monitor the Bell’s Sparrow population since 1999.
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First recognized as a sub-species in the late 1800s (Grinnell 1897, Ridgway 1898), the San Clemente Island Bell’s sparrow was originally called the San Clemente Island sage sparrow (Amphispiza belli clementae). Following an updated taxonomy in 2013, the sage sparrow species was split into Bell's sparrow and sagebrush sparrow, thus re-naming the San Clemente endemic as the San Clemente Island Bell’s sparrow (Artemisiospiza belli clementeae; Chesser et al. 2013).

Bell's sparrow chicks in nest

The San Clemente Bell’s sparrow is 13-15 cm long with a brown back, dusky streaking on the sides, and buffy underparts. It has a dark breast spot, a white eye ring, white supraloral spots on either side of the bill, and prominent, black and white malar stripes. Juveniles are paler in color and more heavily streaked. Bell’s sparrows are ground foragers and opportunistically consume a variety of plant and insect food items. The San Clemente Island subspecies is non-migratory and typically breeds from February through June, often producing multiple broods.  Nests are placed low in a variety of shrub and cactus species, although boxthorn (Lycium californicum) is the most commonly observed substrate.

Bell's sparrow with color bands

 

 

Originally described as a common island resident (Grinnell 1897, Breninger 1904, Linton 1908, Howell 1917), by the late 1960s surveys suggested a small population (Miller 1968, Byers 1976). Following an estimate of only 93 individuals within 740 ha of habitat, the subspecies was listed as threatened under the Endangered Species Act in 1977 (USFWS 1977). Low population levels were attributed to degradation of nesting habitat by non-native feral grazers, and predation by non-native mammalian predators (USFWS 1977). The U.S. Navy, which gained ownership of SCI in 1934, conducted a feral grazer eradication program that was successfully completed in 1993 (U.S. Dept. of the Navy, Southwest Division 2002) and non-native predators are currently managed. Following the eradication of grazers, the island’s native vegetation, including the shrub cover used by nesting Bell’s Sparrows, has been recovering.

West side sparrow habitatIn the early 1990s Bell’s sparrows were mainly limited to boxthorn dominated habitat found along the northern part of the island’s west shore. Surveys conducted in this area from 2000–2012 showed fluctuating numbers of Bell’s sparrows, possibly due to rainfall patterns, but generally reflected an increasing population (Ehlers et al. 2012). Exploratory survey efforts over a larger area from 2010-2012 indicated that birds had spread to other areas of the island, likely as a result of the recovery of vegetation (Ehlers et al. 2011, 2012).

In 2013, IWS began conducting more extensive breeding season surveys in order to systematically assess current Bell’s sparrow distribution and population size. Results from 2013 and 2014 show that the Bell’s sparrow population has increased and sparrows currently occupy much of the island and nest in a variety of habitat types (Meiman et al. 2014a, 2014b). The highest density of sparrows remains in the historically monitored boxthorn habitat, but moderate to high population densities are also found in sagebrush and shrub habitat near canyons and along the steep eastern slope. Sparrows are present in lower densities in mixed shrub, cactus and grassland habitats along the central plateau (Meiman et al. 2014a, 2014b). Recent data also suggests that nesting success is relatively high island-wide (Meiman et al. 2014a, 2014b). IWS continues to monitor the expansion and distribution of the Bell’s sparrow population across the entire island.

Maritime desert scrub on San Clemente

Literature Cited

Breninger, G. F.  1904.  San Clemente Island and its birds.  The Auk 21:218–223.

Byers, S. J.  1976.  Sage sparrow population status survey San Clemente Island. Unpublished report for the U.S. Navy, Navy Region Southwest, Natural Resources Office, San Diego, California.

Chesser, R. T., R. C. Banks, F. K. Barker, C. Cicero, J. L. Dunn, A. W. Kratter, I. J. Lovette, P. C. Rasmussen, J. V. Remsen, J. D. Rising, D. F. Stotz, and K. Winker.  2012.  Fifty-third supplement to the American Ornithologists’ Union check-list of North American birds.  The Auk 129:573-588.

Ehlers, S. E., L. S. Duval, A. S. Bridges, B. Hudgens, and D. K. Garcelon.  2012.  Population monitoring of the San Clemente sage sparrow - 2011.  Final Annual Report.  Unpublished report prepared by the Institute for Wildlife Studies for the United States Navy, Naval Base Coronado, Natural Resources Office, San Diego, California.

Ehlers, S. E., L. S. Duval, A. S. Bridges, B. Hudgens, and D. K. Garcelon.  2013.  Population monitoring of the San Clemente sage sparrow - 2012.  Final Annual Report.  Unpublished report prepared by the Institute for Wildlife Studies for the United States Navy, Naval Base Coronado, Natural Resources Office, San Diego, California.

Grinnell, J. 1897. Report of the birds recorded during a visit to the islands of Santa Barbara, San Nicholas, and San Clemente, in the spring of 1897. Pasadena Academy of Sciences Publication.

Linton, C. B.  1908.  Notes from San Clemente Island.  The Condor 10:82–86.

Howell, A. B.  1917.  Birds of the islands off the coast of southern California.  Pacific Coast Avifauna 12:1–127.

Meiman, S. T., E. E. DeLeon, A. S. Bridges, and D. K. Garcelon.  2014.  Population monitoring of the San Clemente Bell’s sparrow - 2013.  Draft Annual Report.  Unpublished report prepared by the Institute for Wildlife Studies for the United States Navy, Naval Base Coronado, Natural Resources Office, San Diego, California.

Meiman, S. T., E. E. DeLeon, A. S. Bridges, and D. K. Garcelon.  2014.  Population monitoring of the San Clemente Bell’s sparrow 2014.  Draft Annual Report.  Unpublished report prepared by the Institute for Wildlife Studies for the United States Navy, Naval Base Coronado, Natural Resources Office, San Diego, California.

Miller, A. H.  1968.  Amphispiza belli clementae, San Clemente Island sage sparrow. U.S. Museum Bulletin 237:1019–1020.

Ridgway, R.  1898.  Descriptions of supposed new genera, species and subspecies of American birds. I. Fringillidae. The Auk 15:223-230.

U.S. Department of the Interior, Fish and Wildlife Service.  1977.  Endangered and threatened wildlife and plants. Fed. Register 42:40682-40685. U.S. Department of the Navy, Southwest Division. 2002. San Clemente Island Integrated Natural Resources Management Plan Final, May 2002. San Diego, CA. Prepared by Tierra Data Systems, Escondido, CA.