O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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species was detected from November to March through captures of 401 individuals (Geluso, 2007). 
Cockrum et al. (1996) speculated that Arizona myotis from lower elevations along the Colorado 
River in Mohave County, Arizona, may move upstream to hibemacula at higher elevations. It also 
has been speculated that they may overwinter by hibernating in inconspicuous rock crevices at 
higher elevations (O’Shea et al., 2011a) similar to overwintering habits of big brown bats on the 
eastern slope of the Rocky Mountains (Neubaum et al., 2006) and Alberta, Canada (Kliig-Baerwald 
et al., 2017), and postulated for western bats in general by Twente (1960). 
Warm Season Roosts: Live trees, snags, and buildings are used as warm season roosts by this 
species in Arizona. In northern Arizona, Rabe et al. (1998a) radio tracked 22 adult females and 
found 21 of these bats roosting in ponderosa pine snags and one Douglas fir snag, with one roost¬ 
ing in the attic of a cabin. Thirty adults were radio tagged on the Tonto National Forest of central 
Arizona and tracked to 21 roosts (Lutch, 1996). Fourteen roosts were located in trees, with 11 in 
ponderosa pine snags, two in live ponderosa pines, and one in a living Arizona white oak ( Quer- 
cus arizonica ); four roosts were in buildings, one was behind a board on a fencepost (used once by 
a solitary non-reproductive female), and one in a utility pole. The trees used for roosts averaged 17 
meters in height (range 6.2 to 30 meters) and were taller than the average height of trees in the sur¬ 
rounding stand, with heights of roost openings averaging 9.8 meters (range five to 16.5 meters) and 
openings variable in aspect (Lutch, 1996). Two roosts were discovered by tracking a male, who 
roosted alone under loose bark of a ponderosa pine and in a crack in the trunk of an alligator juniper 
(Juniperus deppeana ). Maternity colony size in the attic of a house used by several tagged bats 
ranged 20-51 individuals, and over 100 used one bam, with 35 counted in a second bam; 13 bats 
roosted in the utility pole (Lutch, 1996). Mean colony size at roosts (including trees) used by ten 
tagged individuals was 86 ± 29.6 (SE) bats, but one colony in a ponderosa pine snag numbered 325 
bats. Some roosts were not used in the following year, and many roosts were not occupied consis¬ 
tently in a single season. Ten tagged bats switched roosts every 1.9 ± 0.27 (SE) days (Lutch, 1996). 
Arizona myotis {n = 20 females) radio tracked in east-central Arizona ponderosa pine forest roost¬ 
ed in 22 snags (20 in ponderosa pine, two in Douglas fir), with mean colony sizes of 152 bats 
observed in exit counts (range up to 305; Saunders, 2015). 
Roost use by individual bats can sometimes be quite variable. One of five reproductive 
females radio tracked at Mesa Verde National Park in southwestern Colorado used multiple roosts 
during a summer, including a rock crevice, a ponderosa pine snag, and a building in the nearby, 
lower elevation, irrigated Mancos Valley. The remaining four bats roosted only in buildings in the 
valley and were located an average of 6.8 ± 5.3 (SD) kilometers from points of capture (O’Shea et 
al., 2011a). Five reproductive females captured while foraging at the Bosque Del Apache Nation¬ 
al Wildlife Refuge were radio tagged, with three maternity colony sites and four solitary bat roosts 
discovered (Chung-MacCoubrey, 1999). Two colonies, one composed of over 500 bats and one of 
about 90 bats, roosted under sloughing bark of dead cottonwood trees (Populus fremontii) killed by 
fire, as did four solitary individuals in smaller trees. The roost of a third colony was in a church 13 
kilometers north of the refuge and housed over 1,800 individuals of both Arizona myotis and Yuma 
myotis combined (Chung-MacCoubrey, 1999). 
Colonies of Arizona myotis with numbers as high as the thousands are well-known to roost in 
human-made structures. A maternity colony of about 800 was reported roosting in multiple small, 
vertical crevices under a wooden bridge in the Lower Colorado River Valley of southern Califor¬ 
nia during spring and summer months of 1939 (Stager, 1943b). The bridge also was used by Brazil¬ 
ian free-tailed bats and Yuma myotis (M yumanensis ), species commonly found to share roosts. A 
lone male also was found in a ‘shallow pocket’ in the rock wall of an abandoned mine in the River¬ 
side Mountains in the same region (Stager, 1943b). In New Mexico, a colony of unreported size 
