O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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in northeastern Utah (Hardy, 1941; Twente, 1960). Western small-footed myotis were mostly seen 
hibernating in small numbers in abandoned mine tunnels in Nevada, where they roosted on ceiling 
surfaces and not within deep crevices (Alcorn, 1944). They were one of the more commonly found 
species hibernating in abandoned mines in Great Basin desert scrub and pinon-juniper woodlands 
of the White and Inyo Mountains in California and southwestern Nevada, where they were seen 
hibernating as single individuals, often within crevices, and not in clusters (Szewczak et al., 1998). 
Similar findings were reported for abandoned mines used as hibemacula in west-central Nevada, 
where these bats were found hibernating at air temperatures averaging 5.2°C (range 1.0 to 17°C) 
and at a mean relative humidity of 48% (range 24 to 66%; Kuenzi et al., 1999). Also in Great Basin 
desert scrub, hibernating individuals used six of 31 lava tubes examined in Idaho, where they 
wedged themselves into crevices in the ceilings and were observed in hibernation in various caves 
at air temperatures ranging from 0.9 to 4.7°C (mean 2.4°C) and levels of relative humidity ranging 
from 62 to 85% (Genter, 1986). In Washington and Oregon, these bats were the second most fre¬ 
quently encountered bat found hibernating in searches of 650 caves or mines during winters 1982- 
1989, with 35 found at nine caves and one mine, with one to six bats per site roosting singly 
(Perkins et al., 1990). One was found apparently hibernating in a stone comice of a building in Ore¬ 
gon during November (Perkins et al., 1990). 
Western small-footed myotis have been observed hibernating in a mine at 2,895 meters in 
southwestern Colorado (Armstrong et al., 1994). Small numbers also hibernate in irrigation tunnels 
in northeastern Colorado (Armstrong et al., 1994) and in an abandoned copper mine in southeast¬ 
ern Colorado (Ellinwood, 1978). A survey during 1969-1970 reported them hibernating in num¬ 
bers ranging from one to at least 20 in seven caves and mines ranging from 1,158 to 1,615 meters 
elevation in the Black Hills of South Dakota; bats wedged themselves into tiny crevices and were 
mostly solitary, but with up to four within a crevice (Martin and Hawks, 1972). In winter, counts 
of this species during hibernation at Jewel Cave were 20 or fewer, amounting to less than 1% of all 
hibernating bats of at least seven species seen in the cave over the course of multiple winters 1967- 
1993 (Choate and Anderson, 1997). 
Western small-footed myotis were seldom encountered flying in winter at low-elevation arid 
areas in southern and central New Mexico, representing just 1% (four individuals) of 401 bats of 
12 species documented in winter activity surveys (in contrast, 59 California myotis were captured 
from November to March); three of the four western small-footed myotis were taken in March and 
had been feeding (Geluso, 2007). Winter activity of this species was also detected acoustically dur¬ 
ing warmer periods on prairies in southern Alberta, Canada (Lausen and Barclay, 2006). 
Although most searches for hibernating western small-footed myotis have concentrated on 
caves and mines, relatively small numbers have been detected in such roosts. We suspect that in 
many areas these bats hibernate in inconspicuous rock crevices, similar to big brown bats ( Eptesi- 
cus fuscus) in Colorado (Neubaum et al., 2006) and Alberta, Canada (Kliig-Baerwald et al., 2017), 
and as postulated by Twente (1960) for western bats in general. These bats roost in rock crevices 
during summer (see below), winter flight activity has been documented near known summer 
crevice roosts (Lausen and Barclay, 2006), and the closely related eastern small-footed myotis has 
been found to roost in rock crevices during summer and months immediately prior to or after win¬ 
ter (see below). A single individual was captured and radio tagged at Yellowstone National Park in 
early autumn 2011 and only used rock crevices near the ground until the transmitter likely failed 
in mid-October (Johnson et al., 2017). 
Warm Season Roosts in Rock and Soil Crevices and Cavities: Summer roosting habits of 
western small-footed myotis have not been widely studied, but identified roosts include rock 
crevices and erosion cavities. Tuttle and Heaney (1974) searched by eye and hand for roosts in the 
Badlands of South Dakota during July 1972 and found 12 active roosts occupied by 27 individu- 
