Bat Inventories in the San Francisco Bay Area
Big brown bat in flight. Photo courtesy of Merlin D. Tuttle © Bat Conservation International.
Photo courtesy of Merlin D. Tuttle © Bat Conservation International.

The National Park Service has initiated a program to inventory all plants and animals within the national parks. Several parks in the San Francisco Bay area are among the first to begin field work. Gary Fellers of USGS is conducting the bat inventories at Point Reyes National Seashore, Golden Gate National Recreation Area, Eugene O'Neill National Historic Monument, and John Muir National Historic Monument.

One technique for inventorying bats is to use automated recording stations to record bat vocalizations. Ten of these stations are currently in operation. Each station records ultrasonic sounds throughout the night, every night. Vocalizations are stored on a computer hard drive, or on a Compact Flash Card. Since call files are small, a year's worth of calls can be stored on one CD. Prototype software has been developed that allows for the identification of most species of bats that might occur in the region. As improvements are made in the software and/or the filters used to identify each bat species, the archived call files can easily be reanalyzed.

Information gained from this research will not only result in a more complete inventory of bats, it will provide insights into seasonal activity, habitat preference, and the influence of weather, notably temperature and humidity.

Bat Vocalizations

Bats produce a variety of vocalizations that are used for navigation, feeding, and social communication. Most vocalizations are pitched well above the range of human hearing and are referred to as ultrasonic. These calls are often known as echolocation calls since bats use the echoes produced when a sound bounces off a bug or a building to determine what is in the area. Select a vocalization type from the list below to hear examples of the calls.

Last update: 19 March 2003