56 
PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, Supplement I 
Although evidence of abandonment and limitation of roost use after disturbance is consistent 
across regions in this species, Townsend’s big-eared bats are known to sometimes tolerate certain 
kinds of disturbance: for example, a maternity colony consistently forms each year inside a noisy 
highway structure in Colorado (Siemers and Neubaum, 2015). Levels of disturbance are variable, 
with those involving direct vandalism or killing obviously the most egregious. In contrast, some 
long-term winter surveys and carefully conducted capture and marking efforts at maternity 
colonies have not resulted in obvious indications of roost abandonment or avoidance by 
Townsend’s big-eared bats (Siemers and Neubaum, 2015). 
Managing and Gating of Mines and Caves: Abandoned mines are dangerous to humans. In 
the recent past, public and private land managers sealed or destroyed openings to likely thousands 
of abandoned mines in the interest of public safety; it is thought that these actions had a major neg¬ 
ative impact on populations of Townsend’s big-eared bats throughout their distribution (Pierson et 
al., 1999). During the 1990s resource managers expanded programs to determine the use of mines 
by bats and to secure the entrances of those discovered to be roosts with structures that exclude 
people but allow bats access. Recreational disturbance of caves and abandoned min es is another 
major factor implicated in declines in populations of this species, and visitor restriction through 
gating is the most obvious management action that can address this problem as well. 
Townsend’s big-eared bats are among several species of bats that have been shown to use 
caves and mines with entrances secured by gates or in some cases cable-netting (for example, Pier¬ 
son and Rainey, 1998a; Currie, 2000a; Navo et al., 2000; Sherwin et ah, 2002). Spacing of bars of 
gates placed at entrances of old mines or caves used as roosts by this species such that openings 
are at least 15 centimeters high and 50 centimeters wide has been recommended; these dimensions 
maximize chances of acceptance by bats while maintaining goals of minimizing intrusions (Pier¬ 
son et ah, 1991; Navo, 2001; Sherwin et ah, 2009). Townsend’s big-eared bats have accepted alter¬ 
native, gated roost sites in old mines in cases where previously used mines nearby had to be closed 
(Pierson, 1989; Enderlin, 2000); increased use of roosts by these bats subsequent to installation of 
protective gates also has been documented (Pierson and Rainey, 1998a). When closures of mines 
are necessary, such activities should be carried out at times when bats will not be entombed with¬ 
in them. The State of Colorado has a productive program and well-developed protocols aimed at 
determining use of inactive mines by bats, and these protocols have a strong focus on conservation 
of this species (Navo et ah, 2000; Navo 2001). Over 300 inactive mines used by this species have 
been fitted with bat-compatible closures in Colorado (Annear, 2000). The National Park Service 
has utilized bat-compatible closure methods at abandoned mines used by this species at multiple 
sites around the U.S. (Burghardt, 2000). 
Kretzmann (2002) described gate designs that have been used for protection of Townsend’s 
big-eared bats at abandoned mines in New Mexico. Dozens of mines have been protected with 
gates or cable-netting in New Mexico with positive results (Pierson et ah, 1999). Sherwin et ah 
(2002) review complexities in the use of gated mines by bats, and suggested that culvert/gate com¬ 
binations and other designs can be effective and readily accepted by these bats. However, gating of 
entrances to occupied abandoned mines can affect behavior, especially soon after gates are 
installed. Diamond and Diamond (2014) reported higher rates of circling behavior in maternity 
colonies (averaging 84 to 112 individuals) during morning returns to gated mines in Utah, partic¬ 
ularly at newly gated mines. They also documented greater crowding at emergence time, and more 
collisions with gates (presumably most collisions involving newly volant young) with the latter 
potentially increasing susceptibility to ground predators (Diamond and Diamond, 2014). Nonethe¬ 
less, study authors suggest that these negative behavioral effects are likely outweighed by the pos¬ 
itive effects of enhanced roost protection. In an analysis of the effects of bat gates on multiple 
species, Tobin (2016) concluded that Townsend’s big-eared bats continued using gated mines over 
