Site Fidelity of a Coastal Cactus Wren (Camphylorynchus brunneicapillus) on the Palos Verdes Peninsula

Abstract

The coastal cactus wren (Camphylorhnchus brunneicapillus) is a charismatic, though sedentary bird that inhabits thickets of prickly pear (Opuntia littoralis and O. oricola) and coastal cholla (Cylindropuntia prolifera) in the coastal sage scrub and chaparral habitats of southern California and Baja California, Mexico1 (Rea and Weaver 1990). Urbanization that took place during the past century, with its attendant habitat loss, has deleteriously impacted this species. On the Palos Verdes Peninsula, coastal cactus wrens occupy cactus habitat contained within the five-hectare Palos Verdes Nature Preserve (Preserve) and undeveloped tracts interspersed between the Preserve and urban development. As such, it is an isolated population that faces threats through loss of genetic diversity. Recently, two independent investigations have converged to demonstrate a remarkable instance of site fidelity by a single individual. During 2012 and 2013, biologists from the U. S. Geological Survey sampled 620 coastal cactus wrens in Ventura, Los Angeles, San Bernardino, Riverside, Orange, and San Diego Counties to assess the impacts of habitat fragmentation using contemporary genetic analysis (Barr et al. 2015). Birds that were captured for the genetic analysis were banded to prevent re-sampling individuals1. A total of eight individuals were captured and banded in the Preserve during the second year of this study. Each individual’s location and band number was recorded at capture and blood was drawn for the genetic analysis. In 2014, the Palos Verdes Peninsula Land Conservancy (Conservancy) initiated a Citizen Science Cactus Wren program to utilize volunteers to observe the coastal cactus wrens within the Preserve. The Conservancy manages and restores habitat within the Preserve for several special status species, as well as the coastal cactus wren. The program was designed to return information about how the wrens utilized their habitat, within both existing habitat and newly established areas of habitat. This is important information for the Conservancy in its mission to restore cactus stands within the Preserve’s coastal sage scrub habitat. The volunteers conducted weekly surveys within the Preserve’s Alta Vicente Reserve from March through July during the breeding seasons in 2014 and 2015. The surveys were conducted for 20 minute periods at specifically delineated territorial polygons within areas referred to as West and East (Fig. 1). Observations were recorded by the minute and included number of cactus wrens (adult, juvenile, or unknown), presence of predators, and several qualitative behavior patterns from which frequencies could be computed (Table 1). For these surveys, the enthusiastic volunteers took to the field outfitted with binoculars, spotting scopes, and cameras equipped with telephoto lenses. That coastal cactus wrens spend most of their time moving within the cactus thickets, rising above the cactus for only brief moments, is reflected by the data collected by the Citizen Science