O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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kilometers from roosts) and were triangulated to mountain mahogany, juniper, and ponderosa pine 
habitats with greater frequency than the abundant scrub habitats, although concentrated foraging 
was also observed in sparsely vegetated lava trenches where moths were visibly abundant (Pierson 
and Fellers, 1998). Radio-tagged bats foraged over areas that had been subject to a controlled burn 
at comparable frequencies as over unburned areas (Pierson and Fellers, 1998). On Santa Cruz 
Island in the California Channel Islands, six radio-tagged Townsend’s big-eared bats moved at 
about 30 kilometers per hour during nightly foraging, with some moving over four kilometers from 
the roost; foraging was concentrated along slopes with native vegetation including coastal sage 
scrub oak ( Quercus dumosa ), coast live oak ( Quercus agrifolia ), ironwood (. Lyonothamnus flori- 
bundus ), and hollyleaf cherry (Prunus ilicifolia ) rather than areas with non-native vegetation 
(Brown et al., 1994). The foraging period lasted about three hours, followed by a night-roosting 
period in shallow caves in the foraging area, and a short foraging period prior to returning to the 
day roost in a building (Brown et al., 1994). 
Studies of all U.S. subspecies of Townsend’s big-eared bats suggest insects of the order Lepi- 
doptera are the primary component of the diet, particularly noctuid and sphingid moths, but other 
prey groups are also taken, including coleopterans, dipterans, and hemipterans, (Ross, 1964, 1967; 
Whitaker et al., 1977, 1981; Dalton et al., 1986; Sample and Whitmore, 1993; Burford and Lacki, 
1998; Leslie and Clark, 2002; Ober and Hayes, 2008; Van Den Bussche et al., 2016). Dietary analy¬ 
sis of stomach contents of Townsend’s big-eared bats from northwestern Colorado indicated that 
trichopterans were the dominant dietary component, followed by lepidopterans, dipterans, and 
hymenopterans at proportionally equal frequencies (Armstrong et al., 1994). Based on analysis of 
digestive-tract contents of individuals sampled from New Mexico and Arizona, Ross (1964, 1967) 
suggested that most lepidopterans taken were small, in the three to 10 millimeters length range. In 
West Virginia and eastern Kentucky, many of the moths used as prey by the Virginia big-eared bat 
had forest trees as host species rather than grasses or herbaceous vegetation, and several of the prey 
species were considered forest pests (Sample and Whitmore, 1993; Burford and Lacki 1998). It is 
uncertain if this also is true for the more western subspecies. 
Roosting Habits. — Townsend’s big-eared bats are cave dwellers that typically roost sus¬ 
pended from open cave ceilings or high walls rather than retreating into fissures and crevices with¬ 
in caves (Pearson et al., 1952). They are also found in abandoned mine tunnels (this has been 
known for well over a century; for example, Grinnell and Swarth, 1913), rock shelters and under 
boulders and crevices on cliffs near the ground (for example, Ives, 2015), occasionally in old build¬ 
ings (for example, Bailey, 1936; Dalquest, 1947a; Swenson and Shanks, 1979; Brown et al., 1994) 
and basal hollows of trees (Fellers and Pierson, 2002; Mazurek, 2004). It has been reported that in 
California old mines provide an important proportion of maternity and hibernation sites (Altenbach 
and Pierson, 1995; Pierson et al., 1999), and in Colorado most known roosting sites are also in old 
mines (Belwood and Waugh, 1991). In a 1996-1998 survey that included winter, spring, summer, 
and autumn seasons, 676 abandoned mines and 39 caves in northern Utah were searched for 
Townsend’s big-eared bats (Sherwin et al., 2000). These bats were found in a higher proportion of 
available caves in comparison to mines, and none were found roosting in 105 bridges that were also 
examined. The lack of known long-distance seasonal movements away from roosts (see below) 
may limit local populations of Townsend’s big-eared bats to areas with cavernous geological sub¬ 
strates (for example, karst or lava tubes) or to mining districts, unless roosting behavior patterns in 
alternate roosting structures have become established. Use of specific roosts is dependent on the 
favorability of their thermal regimes and the likelihood of disturbance. 
Winter Roosts: In winter, Townsend’s big-eared bats hibernate in caves and mines, both 
singly and in small clusters of mixed sexes, with the numbers counted within any single hibemac- 
