O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
153 
Fringed myotis were among the species sampled by Adams et al. (2003) that seemed to prefer 
drinking at watering places with higher concentrations of calcium and other minerals; these min¬ 
eral-rich drinking sites perhaps providing a supplement to dietary intake that would be most criti¬ 
cal to reproductive females and weaned volant juveniles. 
Roosting Habits. — Early literature suggests that these bats primarily roost in colonies in 
caves and buildings (for example, Miller and Allen, 1928; Bailey, 1931). More recent research indi¬ 
cates that during warmer months fringed myotis also roost in trees and snags or rock outcrops and 
cliff faces, with the seeming preference for roosts in rock substrates versus trees varying from study 
to study, perhaps depending on roost availability. 
Winter Roosts: In Washington and Oregon, these bats were infrequently encountered in hiber¬ 
nation during searches of 650 caves or mines during winters 1982-1989, with only two found (one 
at each of two mines; Perkins et al., 1990). Two hibernating females were reported from an aban¬ 
doned mine in Mohave County, Arizona, with two hibernating males found in a second mine at 
2,134 meters elevation (Cockrum et al., 1996). Although this bat was often captured in mist nets 
over water in Mohave County during non-winter months, no captures in mist nets were recorded 
during the months of December through April (Cockrum et al., 1996). Two fringed myotis were 
found hibernating in an abandoned copper mine in southern Colorado (Ellinwood, 1978). At Jewel 
Cave in the Black Hills of South Dakota, they roosted singly high on walls in a large chamber dur¬ 
ing winter (Martin and Hawks, 1972), with only up to 10 positively identified during winter counts 
(Choate and Anderson, 1997). 
Mist netting of bats during winter months in central and southern New Mexico yielded only 
one fringed myotis (in November), although intermittent activity of 11 other species was detected 
from November to March by captures of 401 individuals (Geluso, 2007). Given the use of rock 
crevices as roosts during summer and the lack of observations of large numbers of hibernating indi¬ 
viduals observed in caves and mines during winter, it is possible that this species may hibernate in 
inconspicuous rock crevices and fissures as reported for big brown bats in Colorado (Neubaum et 
al., 2006) and Alberta, Canada (Kliig-Baerwald et al., 2017), and as was postulated by Twente 
(1960) for some bats in Utah. 
Warm Season Roosts in Trees and Rock Substrates: Studies of warm-season roosting habits 
of fringed myotis based on radio tracking have been conducted in several regions, including the 
Pacific Northwest, the southwestern states, the central Rocky Mountain states, and western South 
Dakota. Lacki and Baker (2007) tracked 25 females in xeric habitats of eastern Oregon and Wash¬ 
ington. Females often roosted solitarily or with a single pup. Ninety-three per cent of 118 roosts 
were in rock crevices and the remainder in snags and downed logs of ponderosa pine trees. Preg¬ 
nant females tended to choose horizontal rock crevices, whereas lactating females tended to use 
vertically oriented crevices. Bats used the same roost every 1.8 days on average (range one to 16), 
with alternate roosts usually within one kilometer of previous roosts. Snags used as roosts were 
larger and taller than surrounding trees. Although rocks were used as roosts far more frequently, 
snags held the largest groups (up to 118 bats) counted at emergence (Lacki and Baker, 2007). 
In Douglas fir forest in northwestern California, nine radio-tagged fringed myotis of different 
sex and age classes were radio tracked to 52 day roosts, all located in 23 snags (Weller and Zabel, 
2001). Average size of groups emerging from 17 roosts on multiple nights was 31 ± 5 (SE) bats 
(range one to 88); bats switched roosts after 1.7 consecutive days, with roosts used consecutively 
ranging from seven to 641 meters apart (Weller and Zabel, 2001). Snags used as roosts all were in 
early to medium stages of decay, with 20 in Douglas fir snags, one in a ponderosa pine snag, and 
one in a sugar pine (Pinus lambertiana ) snag. Snags used as roosts were taller and had greater girth 
than snags at random sites and were taller relative to canopy height (Weller and Zabel, 2001). In 
