Common Name
Townsend's Big-eared Bats

Scientific Name
Corynorhinus townsendii

Conservation Status
Townsend's big-eared bats are listed as an Endangered species in Washington, a Sensitive species in Oregon, a Species of Special Concern in Texas, Montana and California, and are on the Blue List in British Columbia.

Habitat
They prefer open roosting areas in large rooms and do not tuck themselves into cracks and crevices like many bat species do.

Additional Information

Townsend's big-eared bats are medium-sized, light brown bats with very large ears. They specialize in eating moths and other insects. They occur throughout the Western U.S. and use a variety of habitats, almost always near caves or cave-like roosting areas. They prefer open roosting areas in large rooms and do not tuck themselves into cracks and crevices like many bat species do. Their preference for open spaces in caves makes them easy to detect and vulnerable to vandalism.

Summer maternity colonies range in size from a few dozen to hundreds of individuals. These colonies form between March and June (depending on climate), with pups born between May and July. Maternity colonies choose sites that have warm, stable temperatures for pup rearing. Males remain solitary during the maternity season. Winter hibernation colonies are comprised of males and females and range in size from a few individuals to several hundred bats.Townsend's big-eared bats are very sedentary, with movement by females during the nursing season rarely exceeding 15 km., and movement at other times usually being less than 50 km. If undisturbed, colonies will occupy the same site indefinitely.

Status

Townsends big-eared bats occur throughout the Western U.S from Texas to British Columbia, from sea-level to over 10,000 feet. Distribution is strongly correlated with the availability of caves and cave-like roosting habitat, with population centers occurring in areas dominated by exposed, cavity forming rock and/or historic mining districts. They are generally in decline in most areas, and are listed as an Endangered species in Washington, a Sensitive species in Oregon, a Species of Special Concern in Texas, Montana and California, are on the Blue List in British Columbia ('rare or uncommon, and may be susceptible to large-scale disturbances'). They are considered Sensitive by the U.S. Forest Service.

A study sponsored by the California Department of Fish and Game in the late 1980's documented a population decline of between 40 and 60% in the past 30 years. Only about half of the maternity colonies known to exist in California prior to 1980 were relocated by 1991, resulting in an estimated 54% decline of adult females. Only three maternity colonies increased in size during the period, and all three are located in National Park areas (Point Reyes National Park, Lava Beds National Monument, and Pinnacles National Monument). Of the 23 roosts that are no longer available to bats, 9 (mostly buildings) have been demolished, 4 (all buildings) have burned, 4 (all buildings) have been renovated in such a way that bats were excluded, and 6 (including buildings, caves, mines, and a water diversion tunnel) have had the entrance closed.

Threats

The primary threat to C. townsendii is almost certainly disturbance or destruction of roost sites (e.g., recreational caving, mine reclamation, renewed mining in historic districts). Surveys conducted in Oregon and California indicate that historic roost sites have been negatively impacted in recent years with most reported colonies exhibiting moderate to sizable reduction in numbers. Additional surveys in Utah indicate that several historic maternity sites have been abandoned, although it is not known if these colonies have relocated.

This species is very sensitive to disturbance events and has been documented to abandon roost sites after human visitation. In California and at a number of sites in the east, depressed populations have recovered with the protection (i.e., gating) of roosts. In large portions of its western range, dependence upon abandoned mines puts this species at risk if mine reclamation and renewed mining projects do not mitigate for roost loss, or do not conduct adequate biological surveys prior to mine closure. Both roosting and foraging habitat my be impacted by timber harvest practices. Pesticide spraying in forested and agricultural areas may affect the prey base.

Townsend's big-eared bats on Santa Cruz Island 

Townsend's big-eared bats were first observed on Santa Cruz Island in the historic 2-story ranch house at Prisoner's Harbor in 1939. At that time the maternity roost was estimated to contain "well over 300" individuals. During the mid-1960's UCSB researchers found the colony still active at Prisoners, but this building was removed around that time. Despite extensive searching from 1974 to 1988, no other big-eared bats were seen on Santa Cruz.

In 1991 Dr. Pat Brown of UCLA was made aware of a colony of Townsend's roosting in the bakery room of the Scorpion adobe building. This room was closed until 1984, so it is unknown whether or not there was a maternity colony on the island between the period when the Prisoners' building was lost and the Scorpion bakery room was opened. Dr. Brown believes that prior to building construction, natural caves and rock formations served as roost sites.

Dr. Brown's research in the early 1990's included radio-tracking of bats mist-netted at the Scorpion colony in the late summer of 1992. (Bats were netted at the end of the maternity season when young bats were old enough to fly on their own.) Radio-tracking showed that the Scorpion bats foraged up to 5 kilometers away to feed on moths and other insects among the native oak and ironwood forest on the north-facing slopes of Scorpion Canyon, returning to the roost each morning. She found that the bats used shallow rock caves as night roosts but rarely as day roosts, and no reproduction was noted from these cave areas.

Bi-annual emergence counts (May and August) and visual surveys of the bakery colony conducted since 2002 indicate that a large maternity colony continues to use the building between April, when the room is made available, and at least early September. According to the 1994 Department of Fish and Game report, the Scorpion roost is one of only two or three coastal maternity colonies known to exist south of Pt.

• British Colombia, Ministry of Environment, Land and Parks. 1998. Wildlife at Risk: Townsend's Big-eared Bat. Victoria, B.C. 6 pp. Excellent summary.
• Brown, P.E., R. Berry and C. Brown. 1994. Foraging behavior of Townsend's big-eared bats (Plecotus townsendii) on Santa Cruz Island. in: W.L. Halvorson and G.J. Meander, editors. The Fourth California Islands Symposium: Update on the Status of Resources. Santa Barbara Museum of Natural History, Santa Barbara, CA.
• National Park Service, Pinnacles National Monument. 2003. Finding of No Significant Impact, Bear Gulch Cave Management Plan. 6 pp.
• Pierson, E.D. and W.E. Rainey. 1998. Distribution, status, and management of Townsend's big-eared bat (Corynorhinus townsendii) in California. BMCP Technical Report #96-7, submitted to State of California, The Resources Agency, Department of Fish and Game. 36 pp.