Effects of Urbanization on Activity and Diversity of Southern California Bats

Habitat loss and fragmentation threaten wildlife populations at urban-wildland interfaces. Urbanization can result in loss of roosting sites and foraging habitat for many bat species. Bat species differ in their ability to tolerate an increasingly developed environment. The factors that allow some bat species to persist in cities and suburban landscapes, while others decline, are unclear. Southern California is home to 14 species of bats, but little is known about how they are affected by urban development. We used a Pettersson D240X detector to monitor bat echolocation calls and assess how species richness and activity differ across four sites in the San Gabriel Valley, that vary in microhabitat features and levels of urbanization. We hypothesized that bat activity and species richness would be low at sites with homogenous microhabitats and in highly urbanized landscapes. Sampling in Spring 2012 revealed high variation in bat activity levels across sites (range: 0.25 - 172.5 passes/hr). Using Sonobat software to analyze calls, we detected the presence of four species across the sites: Lasiurus cinereus, Tadarida brasiliensis, Myotis californicus and Eptesicus fuscus. While species richness was consistent across sites, bat activity was highest at the most urbanized sites. Future sampling will allow us to determine how specific microhabitat and landscape-level characteristics at each site affect bat activity. Sampling will continue throughout Summer 2012 to determine trends in activity levels and species richness across sites. Understanding how bats are affected by the loss and fragmentation of natural habitats will aid in regional bat conservation efforts.