O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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isopterans, and dipterans (Whitaker et al., 1981). Black (1974) observed these bats forage about 
three meters above water in the San Mateo Mountains of New Mexico, occasionally gleaning 
moths off the water surface but having a low proportion of moths or beetles in their diet. This 
species also has been observed regularly foraging low over large eddies and backwaters of major 
rivers in western Colorado, such as the Green, Yampa, and Colorado rivers (Neubaum, 2017). 
Roosting Habits. — Yuma myotis will roost in mines, caves, buildings, bridges, cliff 
crevices, swallow nests, and other structures, typically in fairly close proximity to water (Dalquest 
and Ramage, 1946; Glass and Ward, 1959; Constantine, 1961a). They are known to share roosting 
structures with a number of other species, including Arizona myotis, cave myotis, fringed myotis, 
long-legged myotis, long-eared myotis, California myotis, big brown bats, pallid bats ( Antrozous 
pallidus), and Brazilian free-tailed bats (for example, Dalquest, 1947a,b; Constantine, 1961a; 
Studier, 1968; Geluso and Mink, 2009). Sexes typically roost apart in summer, with males often 
found solitary and females in maternity colonies (Dalquest, 1947b). 
Winter Roosts: Remarkably little information exists on the natural winter roosting habits of 
this widely distributed species (Boyles et al., 2006). Low numbers were observed in hibernation in 
lava caves near Mount St. Helens in Washington during winter months in 1967-1970 (Senger et 
al., 1974). Bridges were found to serve as winter roosts in the central Sierra Nevada of California 
(Pierson et al., 2001). A “few” were reported in winter in an abandoned min e in the Whipple Moun¬ 
tains of San Bernardino County, California (Brown, 2013:12). This species was captured swarm¬ 
ing at a cave at an elevation of 3,000 meters in northwestern Colorado during September, suggest¬ 
ing they may hibernate in the region (Navo et al., 2002). It has been speculated that in Arizona and 
Texas these bats may migrate south for the winter (Hoffmeister, 1986; Schmidly, 1991). Mist net¬ 
ting of bats during winter months in central and southern New Mexico did not yield any bats of this 
species, although intermittent activity of 12 other species was detected with captures of 401 indi¬ 
viduals (Geluso, 2007). Large numbers are known to roost in colonies under bridges (see below) 
in parts of the surveyed area of New Mexico during summer, but only a few were found at these 
same bridges during November through March (Geluso and Mink, 2009). 
Warm Season Roosts in Rock Crevices, Trees, and Swallow Nests: A maternity colony of 
Yuma myotis was found in a sandstone cliff in a vertical southeast-facing crevice about 10 meters 
above ground level in Las Ani mas County in south-eastern Colorado (Ellinwood, 1978). Nineteen 
females (most were reproductive) were radio tracked to 27 roosts in western Colorado: all roosted 
in rock crevices in cliffs (Neubaum, 2017). Maternity colonies found in cliffs during the latter Col¬ 
orado study were variable in size but ranged up to 189 or more individuals (Neubaum, 2017). Small 
(up to 30 individuals) colonies were observed roosting in narrow vertical crevices in limestone 
cliffs in the Verde Valley of central Arizona (Vaughan, 1980). Two solitary individuals each roost¬ 
ed in snags of cottonwood trees ( Populus fremontii ) along the Rio Grande at Bosque Del Apache 
National Wildlife Refuge in New Mexico (Chung-MacCoubrey, 1999), and a single bat was 
observed roosting under bark of a tree stump in southern British Columbia (Vonhof and Barclay, 
1997). 
Radio tracking of individual Yuma myotis of both sexes (colony attributes were not reported) 
captured in summer in a suburban area south of San Francisco Bay in California showed that diur¬ 
nal roosts of these bats were in trees and to a lesser extent buildings (Evelyn et al., 2004). Trees 
used as roosts included both conifers (least redwood, Sequoia semipervens, and Douglas fir) and 
hardwoods (primarily valley oaks, Quercus lobata, coast live oak, Quercus agrifolia, and big leaf 
maple, Acer macrophyllum). Most (16 of 18) of the roost trees were alive. Roosts in live hardwood 
trees included cavities, cracks, and other features in trees with fungal infections, and dead or bro¬ 
ken limbs and tops. Some individual bats switched roosts in trees about every 4.5 days, with a mean 
