Bat Inventory of Eugene O'Neill National Historic Site, John Muir National Historic Site and Point Reyes National Seashore

Photo of a hoary bat
The Hoary Bat (Lasiurus cinereus) is one species documented at Eugene O’Neill, John Muir, and Point Reyes.

USGS / Paul Cryan

The Question

Which bat species are present at Eugene O'Neill National Historic Site, John Muir National Historic Site, and Point Reyes National Seashore? Which bat species utilize different habitats within Point Reyes National Seashore?

Bats are economically and ecologically important animals, providing ecosystem services such as pollination and predation of insects. Most bat species are difficult to study in the wild because of their nocturnal foraging and cryptic, inaccessible roost sites. In general, bat populations are believed to be declining. Most species have very low reproductive rates, producing about one offspring per year. Many species are also constrained by a limited number of specific roosting sites, despite large numbers of individuals in a population. These factors make recovery a slow process.

The declines are likely due to direct and indirect human impacts, primarily through destruction of foraging and roosting sites. The wildland-urban interface, or the intersection between wild and urban areas, is an important location for inventorying and monitoring of bat populations to determine the impacts of human development.

Biodiversity of bats in the U.S. is relatively low (45 species) in comparison to other taxonomic groups. The central coast of California is known to support 17 species from two families, nine of which have special status. All of these species are insectivorous, meaning they rely on insects as a primary food source.

Sample vocalization of a silver-haired bat (Lasionycteris noctivagans) collected through the Anabat II Detector System.
Sample vocalization of a silver-haired bat (Lasionycteris noctivagans) collected through the Anabat II Detector System.


The Project

Use acoustic sampling to conduct bat inventories in three San Francisco Bay Area Network parks.

Bats make ultrasonic vocalizations to communicate and echolocate prey. Researchers can record and analyze these calls using acoustic sampling methods. Acoustic sampling for this project utilized an Anabat II Detector System, which detects the ultrasonic echolocation calls and converts the signals into graphs on a computer. The graph of each call is unique, and can often be used to determine the species based on the frequency, shape, duration, and time interval of the call. Knowledge of the local bat ecology is necessary when analyzing acoustic data.

Acoustic sampling was conducted at Eugene O'Neill National Historic Site, John Muir National Historic Site, and Point Reyes National Seashore. All of these parks are on the wildland-urban interface. One station was installed at both Eugene O’Neill and John Muir. Eight stations were installed at Point Reyes, with one on the Golden Gate National Recreation Area North Unit (administered by Point Reyes) to target a range of habitats. At each station, Anabat II Detector Systems were installed and connected to a computer to collect data every night. Because this system required 24-hour access to 110-volt power, all sample sites were constrained to be on or near structures. Researchers checked the units and downloaded data at least once each month. One station at Point Reyes, the Bear Valley monitoring station, began operating in 1999. All other stations were installed in 2002. Some stations continued to collect data for over four years.


Nine bat species were detected at Eugene O’Neill, John Muir, and Point Reyes. More species may be detected through alternate sampling methods. There were large differences in the number of calls detected at different sampling locations.

The differences in numbers of calls at different locations were likely due to the number of individual bats in the vicinity of the detector, and potentially the activity of a few bats that might be foraging (e.g., flying back and forth) in the vicinity of the detector. There were known bat roosts in the vicinity of the detectors at the Clem Miller Education Center (Point Reyes), Point Blue Conservation Science (Palomarin), and the Wilkins Ranch sites (Bolinas). Interestingly, there was almost certainly not a roost in the vicinity of the detector at Olema Marsh, which detected a fairly large number of calls.

Table 1. Comparison of total number of detected calls and calls per day between sampling locations for 2002-2003 bat inventories.
Park Location Days Total # of Calls Calls per Day
Eugene O’Neill Maintenance barn 386 327,640 848.8
John Muir Maintenance building 423 223,960 529.5
Point Reyes Bear Valley 714 552,367 773.6
Point Reyes Education Center 472 1,849,923 3919.3
Point Reyes Learning Center 299 93,023 311.1
Point Reyes North District Operations Center 333 64,890 194.9
Point Reyes Olema Marsh 424 459,052 1082.7
Point Reyes Point Blue (Palomarin) 317 749,260 2363.6
Point Reyes Point Reyes National Seashore Association 393 174,212 443.3
Point Reyes Shallow Beach 383 208,728 544.9
Point Reyes Wilkins Ranch 480 620,302 1292.3
Figure 1. There were large differences between the numbers of calls dectected at different sampling locations. Detectors at the Point Reyes Education Center and Point Blue sites collected the highest number of calls per day. Graph by Maritte O'Gallagher, NPS.
Visual representation of data in table above, in the form of a bar graph.

Table 2. Table of bat species detectable by acoustic monitoring at each park. Each of these species was detected at Eugene O’Neill, John Muir, and Point Reyes. Special status codes: FS =Forest Service Sensitive species; BLM =Bureau of Land Management Sensitive species; and WBWG =Western Bat Working Group High Priority species.
Scientific Name Common Name Special Status
Myotis lucifugus Little brown myotis ----------
Myotis yumanensis Yuma myotis ----------
Myotis thysanodes Fringed myotis FS, BLM, WBWG
Myotis californicus California myotis ----------
Lasionycteris noctivagans Silver-haired bat ----------
Eptesicus fuscus Big brown bat ----------
Lasiurus blossevillii Western red bat FS, WBWG
Lasiurus cinereus Hoary bat ----------
Tadarida brasiliensis Mexican free-tailed bat ----------

Additional Resources

Fellers GM. 2007. Acoustic Inventory and Monitoring of Bats at National Parks in the San Francisco Bay Area. Western Ecological Research Center, USGS. Point Reyes, CA.

Contact Information

San Francisco Bay Area Inventory & Monitoring Network
Pacific Coast Science & Learning Center
USGS Western Ecological Research Center
San Francisco Bay Area Network Species Lists - Certified Species lists including residency, abundance, and native/non-native status.

Summary by the Pacific Coast Science and Learning Center, April 2006.