O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
49 
many as 90 individuals has been found roosting during warmer months inside a hollow section of 
raised road and bridge on a busy interstate freeway (Siemers and Neubaum, 2015). A reproductive 
female caught over an ephemeral pool in the canyons of Colorado National Monument was tracked 
to a house in an adjacent suburb in the city of Grand Junction, Colorado (Neubaum, 2017). 
Movements From and Among Roosts: Townsend’s big-eared bats are not known to be long¬ 
distance migrants. In an approximately five-year study involving 1,500 banded individuals in Cal¬ 
ifornia, almost all banded bats were found at the same place or within about 2.4 kilometers of the 
site where first banded in previous years; the maximum distance moved by a banded individual was 
32 kilometers in a male (Pearson et al., 1952). In Kansas and Oklahoma, 194 recaptures of 827 
banded bats over a seven- to 11-year study also showed that the species is fairly sedentary: only 16 
bats were recovered at sites other than the place of banding, and 86% of these made movements of 
less than 1.6 kilometers; only two moved to roosts greater than eight kilometers apart (Humphrey 
and Kunz, 1976). Distances between maternity roosts and hibemacula of three bats ranged about 
three to 40 kilometers (Humphrey and Kunz, 1976). Three radio-tagged big-eared bats in central 
Oregon dispersed 11-24 kilometers from the hibemacula in spring (Dobkin et al., 1995). Howev¬ 
er, three females banded during winter in the Black Hills of South Dakota were subsequently recov¬ 
ered at three different localities during summer, all of which were more than 50 kilometers away 
from the hibemaculum (Cryan, 1997). Townsend’s big-eared bats marked with passive integrated 
transponder (PIT) tags at a maternity colony in the mountains of western Colorado were subse¬ 
quently found in a large hibemacula in a cave approximately 50 kilometers from the maternity site 
(Siemers and Neubaum, 2015). 
Switching of roost sites by maternity colonies can occur, somet im es based on temperature 
preferenda at different phases of reproduction and development (Pierson et al., 1999, Sherwin et 
al., 2000). Fellers and Pierson (2002) noted the presence of adult males in a roost comprised most¬ 
ly of females during mid-September. In northern Utah, autumn and spring use of mines and caves 
showed high variability, with frequent movements among different sites (Sherwin et al., 2000). 
This species uses abandoned mines as autumn swarming sites, behavior that appears to be critical 
for mating and maintaining genetic diversity (Ingersoll et al., 2010; Siemers and Neubaum, 2015). 
Some abandoned mines used for swarming are also used as hibemacula, whereas others are used 
exclusively for swarming; temperatures at swarming sites were cool enough for efficient energy 
assimilation, but warm enough to facilitate frequent arousals. At mines used for hibemacula in Col¬ 
orado, the numbers of swarming individuals were positively correlated with numbers that use the 
same sites as hibemacula (Ingersoll et al., 2010). 
Night Roosts: Townsend’s big-eared bats utilize night roosts in caves, mines, small rock shel¬ 
ters, under bridges, buildings, or other sheltered sites. Some night-roosting bats may not return to 
the diurnal roosts until shortly before dawn (Pearson et al., 1952; Pierson et al., 1996b), although 
activity patterns vary seasonally and with stage of reproduction (Pierson et al., 1999). Night roosts 
are sometimes shared with other species. In Colorado, captures at entrances suggest possible use 
of caves as night roosts by small numbers of individuals (one to six) at each cave (Siemers, 2002). 
Similar findings were reported at Oregon Caves National Monument (Albright, 1959). Townsend’s 
big-eared bat is well known to night-roost in buildings (for example, Dalquest and Ramage, 1946). 
Bridges are used by night-roosting individuals, as documented in the central Sierra Nevada of Cal¬ 
ifornia and the Willamette Valley of Oregon (Perimeter, 1996; Pierson et al., 2001). Use of large 
basal hollows in trees as roosts in California apparently also includes use as night roosts (Gellman 
and Zielinski, 1996; Fellers and Pierson, 2002). 
Population Ecology. — Litter Size, Natality, and Female Reproduction: A single off¬ 
spring at birth is well-documented throughout the range of Townsend’s big-eared bat in western 
