The Bell's sparrow (San Clemente) is a subspecies endemic to San Clemente Island (SCI), California. Its' name changed from San Clemente sage sparrow in 2013, when the sage sparrow species was split into Bell's sparrow and sagebrush sparrow. A. b. clementeae was first recognized as a subspecies by Grinnell (1897), and then formally described by Ridgway (1898), who later doubted the validity of his claim. However, subspecies status was supported by van Rossem (1932) and is recognized to this day. The subspecies status of A. b. clementeae was recently challenged because of lack of diagnosability based on one morphometric and two plumage characteristics (Patten and Unitt 2002).
The Bell's sparrow distribution on SCI is mostly limited to the lower elevations of the western slope, where the vegetation is dominated by boxthorn (Lycium californicum); a low thorny shrub. Non-native mammals, such as sheep (Ovis aries), pigs (Sus scrofa), mule deer (Odocoileus hemionus) and goats (Capra hircus) negatively impacted most of SCI’s vegetation types, including boxthorn, starting in the late 1800s. 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).
The first Bell's sparrow surveys yielded low population estimates (Miller 1968, Byers 1976), prompting the U.S. Fish and Wildlife Service to list the subspecies as threatened (U.S. Department of the Interior 1977). Subsequent surveys found the population size to have remained low (Hyde 1980, Mills 1984, Hyde 1985), possibly because of the impact feral grazers had on distribution and cover of woody plants, including boxthorn (Ferguson 1979, Hyde 1985, Resnick 1988). Hyde (1985) suggested that yearly variations in population size are linked to annual rainfall, which affects the amount of resources available to Bell's sparrows.
Since the late 1990s several Bell's sparrow surveys have been conducted. They resulted in higher population size estimates than what had been observed previously. In addition to surveys, since 1999, the Institute has been conducting research on annual productivity and nest success, nest site characteristics, habitat characteristics, territory size and density, and juvenile and adult survival (Munkwitz et al. 2000, 2002a, 2002b, Beaudry et al. 2003). Finally, through Cooperative Research Agreements (CRA) between the U.S. Navy, the Institute for Wildlife Studies and Humboldt State University, a study on the natal and breeding dispersal of the Bell's sparrow (CRA - Munkwitz 2003), along with a population viability analysis (CRA – Beaudry 2003), will be completed.
Continuing methods in use since 1999, we monitored population abundance and reproductive success during the 2003 breeding season. The distribution of study plots and the methods used to characterize habitat and analyze survival were the same as those used in 2002 (Beaudry et al. 2003). We monitored an area of SCI known as TAR 4 as part of an ongoing study of the potential effects of construction and military use on Bell's sparrows.
In contrast to its mainland relatives, which are obligates of sagebrush communities, the Bell's sparrow on SCI has adapted to maritime desert scrub habitat, cactus, and saltbush. The majority of breeding territories are found on the lower, flat terraces between 10 m and 30 m above sea level, although nesting sites have been found as high as 150m above sea level. Nests are typically placed low to the ground in a boxthorn shrub, using the surrounding vegetation as cover.
Beaudry, F., N. M. Munkwitz, E. L. Kershner, and D. K. Garcelon. 2003. Population Monitoring of the San Clemente sage sparrow – 2002, Final Report. Unpublished report prepared by the Institute for Wildlife Studies for the U.S. Navy, Commander Navy Region Southwest, Natural Resources Office, San Diego, California. 69pp.
Byers, S. J. 1976. Sage sparrow status survey San Clemente Island. Report to the U.S. Navy. Unpublished manuscript.
Ferguson, H. L. 1979. The Goats of San Clemente Island. Fremontia 7(3):3–8.
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.
Hyde, K. M. 1980. San Clemente Island Loggerhead shrike/Sage sparrow study, Interim report October 1980. Prepared under contract no. N00246-80M-3994 and -7334 for Natural Resources Office, North Island Naval Air Station, San Diego, California.
Hyde, K. M. 1985. The status of the San Clemente sage sparrow. September 1985. Prepared under contract no. N62474-85-M-4328 for Natural Resources Office, North Island Naval Air Station, San Diego, California.
Miller, A. H. 1968. Amphispiza belli clementae, San Clemente Island sage sparrow. U.S. Museum Bulletin 237:1019–1020.
Mills, J. 1984. San Clemente Island sage sparrow interim study. Prepared for Natural Resources Office, North Island Naval Air Station. San Diego, California.
Munkwitz, N. M., F. Beaudry, G. A. Schmidt, and D. K. Garcelon. 2000. Population monitoring of the San Clemente Sage Sparrow – 1999, Final Report. U.S. Navy, Commander Navy Region Southwest, Natural Resources Office, San Diego, California. 35pp.
Munkwitz, N. M., F. Beaudry, G. A. Schmidt, and D. K. Garcelon. 2002a. Population monitoring of the San Clemente Sage Sparrow – 2000, Final Report. U.S. Navy, Commander Navy Region Southwest, Natural Resources Office, San Diego, California. 58pp.
Munkwitz, N. M., F. Beaudry, and D. K. Garcelon. 2002b. Population monitoring of the San Clemente Sage Sparrow – 2001, Final Report. U.S. Navy, Commander Navy Region Southwest, Natural Resources Office, San Diego, California. 71pp.
Patten, M. A. and P. Unitt. 2002. Diagnosability versus mean differences of sage sparrow subspecies. Auk 119(1):26-35.
Resnick, J. M. 1988. Feral goat foraging and vegetational changes on San Clemente Island, California. Ph.D. Dissertation, Univ. California, Los Angeles, California. 144pp.
Ridgway, R. 1898. Descriptions of supposed new genera, species and subspecies of American birds. I. Fringillidae. 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
Van Rossem, A. J. 1932. On the Validity of the San Clemente Island Bell’s Sparrow. Auk XLIX: 490-491.