46 
PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, Supplement I 
ulum usually not exceeding the hundreds. For example, numbers of hibernating bats observed per 
cave ranged from 0 to 274 in counts at six caves surveyed every other year from 2004 to 2013 on 
Mount St. Helens in Washington (Wainwright and Reynolds, 2013). Observations in abandoned 
mines in western and central Nevada recorded numerous mines each with very small numbers of 
hibernating individuals (Alcorn, 1944; Szewczak et al., 1998; Kuenzi et al., 1999). Seven out of 
260 mines examined by Szewczak et al. (1998) had 19-80 bats each, with the remainder having 
none to a few individuals (Szewczak et al., 1998). Observations in Utah were similar, with one or 
two bats per site when present and a maximum of 13 recorded during winter searches of over 500 
mines and caves (Twente, 1960). Townsend’s big-eared bats were the most co mm on species noted 
during cave and mine surveys in Montana (Hendricks, 2012). A survey in the Black Hills of South 
Dakota during 1969-1970 reported Townsend’s big-eared bats hibernating in total numbers rang¬ 
ing from one to about 1,000 in 15 caves and mines at elevations from 1,158 to 1,917 m; ambient 
temperatures at a subset of these caves and mines varied from three to 12°C, with a mean of 6.1°C 
(Martin and Hawks, 1972). Counts over the past half century at Jewel Cave National Monument in 
the Black Hills consistently number > 600 (Choate and Anderson, 1997; records on file at Jewel 
Cave National Monument). 
The largest number of hibernating Townsend’s big-eared bats counted at a single cave at Lava 
Beds National Monument in northern California, an area with protections and an increasing popu¬ 
lation, was 699 bats in 2004 (Weller et al., 2014). Several l im estone caves at 800-1,200 meters ele¬ 
vation in northern California had solitary individuals and groups of three to 50 Townsend’s big- 
eared bats during winter surveys (Graham, 1966; Marcot, 1984). About 185 bats were document¬ 
ed using nine of 31 lava tube caves examined in Idaho (Genter, 1986). A winter colony of 500-600 
individuals has been consistently observed in a cave in the mountains of Colorado since the late 
1950’s (Siemers and Neubaum, 2015). The largest number observed in hibernation in the western 
United States was 10,000 in a mineshaft in New Mexico discovered by J.S. Altenbach in 1992 
(Pierson and Rainey, 1998a). This species also hibernates in irrigation tunnels in Colorado (Arm¬ 
strong et al., 1994). In addition to use of inactive mines, about 190-200 were observed hibernating 
in clusters of two to 20 individuals in a working gold mine in southwestern Colorado (Armstrong 
et al., 1994). Hibemacula can include several other species of bats. 
Factors associated with use of abandoned mines as hibemacula for Townsend’s big-eared bats 
have been investigated in southwestern Colorado (Ingersoll et al., 2010; Hayes et al., 2011). Hayes 
et al. (2011) found 99 bats hibernating at 38 out of the 133 abandoned mines examined (mean 2.6, 
range one to eight bats per occupied mine, with nearly all bats roosting solitarily). Ingersoll et al. 
(2010) reported a mean of 2.3 hibernating bats at 61 of 158 mines examined. Temperatures near 
hibernating bats averaged 4°C (range -2.6-9.0°C) in the study by Hayes et al. (2011). In one analy¬ 
sis, the mine site variables thought to be most important included temperature at the mine portal 
and number of openings, with other possibly important factors including depth; the most important 
factor believed to influence hibemacula use at a landscape scale was mean annual ambient tem¬ 
perature (Hayes et al., 2011). As in other studies of caves and mines, number of openings was 
thought to be an important variable because the increased air exchange allows bats to take advan¬ 
tage of a greater range of internal temperatures. Ingersoll et al. (2010) also found that increased 
structural complexity of abandoned mines was an important variable in their use as hibemacula by 
this species. 
In a study in Idaho, habitat characteristics associated with use of lava tube caves as hibemac¬ 
ula by Townsend’s big-eared bats were investigated by Gillies et al. (2014). Twenty-four habitat 
variables (including indices of human visitation) were measured at different scales. Compared to 
