Western Birds

Vol. 45, No. 1

March 2014

Western Field Ornithologists

pages 43–56

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A Population Census of the Cactus Wren
in Ventura County, California

Daniel S. Cooper, Linnea S. Hall, and Adam J. Searcy

ABSTRACT

The Cactus Wren (Campylorhynchus brunneicapillus) is a polytypic species widespread in the southwestern U.S. and northern Mexico. Though closer in plumage characteristics to the desert subspecies anthonyi, populations resident in coastal sage scrub on the coastal slope of Ventura County and Los Angeles County occupy an ecological niche more similar to that of the more southerly subspecies sandiegensis. Because of fragmentation of habitat associated with urbanization, the populations on southern California’s coastal slope are almost entirely isolated from those of the deserts, and apparently from each other. They are declining precipitously for reasons not entirely understood but certainly related to loss, fragmentation, and degradation of suitable habitat. In 2012, we organized a volunteer effort to map the entire population in Ventura County and found 111 active, accessible territories with at least one adult or a fresh nest. Additional areas to which we did not have access could raise this total number to 166 territories county-wide. While historically the species occurred somewhat more widely in the eastern portion of the county, all active territories now appear to be restricted to a narrow band of cactus-rich scrub at the far western edge of the Santa Monica Mountains and Simi Hills, from Point Mugu northeast through Thousand Oaks to the west side of Simi Valley, roughly tracking the distribution of large patches of prickly-pear (Opuntia spp.) and coast cholla (Cylindropuntia prolifera).

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