California Gnatcatcher Habitat Analysis and Population Surveys, MCAS Miramar

Museum biologists conducted station-wide surveys and an in-depth habitat and productivity study at Marine Corps Air Station (MCAS) Miramar for the federal and state threatened coastal California gnatcatcher. As surveys for California gnatcatcher have been conducted approximately every three years on MCAS Miramar since 1997, this study contributed to our understanding of the long-term population trends and changing habitat quality in an environment that was substantially altered by the Cedar Fire in 2003.

Biologists conducted protocol surveys and nest monitoring to determine the California gnatcatcher’s population size, distribution, and breeding success within MCAS Miramar. However, this study stands out in its comprehensive approach to assessing and quantifying habitat conditions that may affect the species’ productivity.

Using the California Department of Fish and Wildlife-California Native Plant Society Combined Vegetation Rapid Assessment and Relevé Protocol, the team collected detailed data on topography; vegetation structure, density, and composition; and natural and human-caused disturbance at breeding locations. They recorded air temperatures at a much finer scale than have been recorded previously, taking measurements over time immediately within breeding pairs’ use areas.

Finally, during the nesting season and the non-nesting season, SDNHM’s entomologists sampled eight plant species within California gnatcatcher nesting territories for arthropod diversity and abundance. Although the components of the California gnatcatcher’s diet have been documented previously, very little had been known about how the distribution of preferred prey items relates to individual plant species.

With in-house experts in ornithology and entomology, and the largest entomological reference collection in the region, the San Diego Natural History Museum has a unique ability to conduct such a comprehensive study.