Status of the Cactus Wren (Campylorhynchus brenneicapillus) Within the Coastal Subregion of Orange County, CA

Type: report

Article abstract: In 1993 the Laguna Fire burned 75% of the coastal reserve of the Nature Reserve of Orange County (NROC). From 1999 to 2004, annual monitoring efforts showed the cactus wren population in the coastal reserve declined from an estimated 132 (93) to 55 (40) territories, a 58% decline during the six years. In the same period, the estimated decline in the central reserve was only 26%, a figure consistent with short-term declines documented for other CSS birds, including the California gnatcatcher, during the same period. In 2006, we completed two rounds of focused cactus wren surveys in the coastal reserve, including existing use, special linkages, and non-NROC open space areas. We mapped and classified all cactus-containing habitats within 20 management areas. These surveys found 65 occupied territories within the coastal reserve. Using site occupancy models we estimate 71.4 (�6) territories were present in the surveyed area. Out of 2,323 acres of cactus scrub mapped in 2006, 1,336 acres, or 58%, mostly within the Laguna Fire perimeter appeared to be insufficiently developed for occupancy by cactus wrens. Only 187 acres were found to be occupied, whereas our estimates based on historic data indicate approximately 1,473 acres were occupied in 1992, an 87% decline. Out of eight management areas that held at least 8 territories in 1992, only two areas, Sand Canyon and Turtle Rock, did not show significant declines between 1992 and 2006. Portions of the coastal reserve experiencing significant losses included the Sycamore Hills and Aliso & Woods management areas, both of which did not burn in 1993. Declines in unburned areas may reflect differences in biological productivity, edge effects, and an inability of wrens to disperse large distances. Given the small size of the cactus wren population in the coastal reserve, slow recovery of burned cactus scrub habitat, and significant population declines in unburned areas, this population warrants further focused study and development of a management program that aims toward stabilizing the population in the short-term.

Number of pages: 18

Authors: Hamilton, Robb; Mitrovich, Milan;

Year: 2007

Purpose: Report on methodologies used to survey and census cactus scrub habitat and cactus wren population in the coastal subregion, identify key results, and propose new interpretations for the recently documented wren declines.

Prepared for: Nature Reserve of Orange County;

Prepared by: Nature Reserve of Orange County; Hamilton, Robb;

Keywords: Cactus Wren; Campylorhynchus brunneicapillus; NROC; Orange County;