Distribution, Abundance, and Breeding Activities of the Least Bell's Vireo at Marine Corps Base Camp Pendleton, California

Type: report

Article abstract: Surveys for the endangered Least Bell's Vireo (Vireo bellii pusillus) were conducted at Marine Corps Base Camp Pendleton (MCBCP or Base), California, between 24 June and 11 August 2011. Surveys in 2011 began later than usual (late June vs. late March/early April) because of contract delays. Consequently, data collected in 2011 may not be directly comparable to other years and represents a minimum population estimate. Drainages containing riparian habitat suitable for vireos were surveyed two to three times. A minimum of 784 male vireos and 19 transient vireos were detected on 19 out of the 23 drainages/sites surveyed. Ninety-four percent of all vireo territories occurred on the seven most populated drainages, with the Santa Margarita River containing 60% of all territories on Base. Fifty-seven percent of male vireos were confirmed as paired.

Number of pages: 89

Authors: Lynn, Suellen; Kus, Barbara;

Year: 2011

Purpose: he purpose of this study was to document the status of Least Bell's Vireo at Marine Corps Base Camp Pendleton in San Diego County, California. Specifically, our goals were to (1) determine the size and composition of the vireo population at the Base, (2) characterize habitat used by vireos, (3) band a subset of vireos to facilitate the estimation of vireo survivorship and movement, and (4) assess the short-term effects of giant reed removal on vireo fecundity, nest success, and productivity by intensively monitoring vireos within established nest monitoring sites that had recently undergone giant reed removal (2008) and at reference sites in which giant reed had been removed 11-13 years earlier, between 1997 and 1999. In October and November 2007, wildfires burned a substantial portion of several drainages on MCBCP, including Aliso Canyon, Las Flores Creek, Horno Canyon, Piedra de Lumbre Canyon, San Onofre Creek, and sections of the Santa Margarita River, and in October 2008, a wildfire burned a section of the Pilgrim Creek drainage (Fig. 1). While this project did not include a specific study design to determine the effects of fire on vireos, these data may be used to track vireo response to the fire and post-fire habitat recovery. When combined with data from other years, these data will inform natural resource managers about the status of this endangered species at MCBCP, and guide modification of land use and management practices as appropriate to ensure the species’ continued existence.

Prepared for: Assistant Chief of Staff, Environmental Security U.S. Marine Corps Base Camp Pendleton;

Prepared by: U.S. Geological Survey, Western Ecological Research Center;

Keywords: endangered species; least Bell's Vireo; Marine Corps Base Camp Pendleton;

Species: Least Bell's vireo

Vegetation communities: riparian forest & scrub

Threats: Parasitism/disease