O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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and a colony of about 30 occupied the gable of a bam near Sutcliffe, Nevada in 1926 (Hall, 1946). 
About 100 individuals roosted beneath an awning on a building in El Centro, Imperial County Cal¬ 
ifornia during October (Howell, 1920a), a maternity colony of 1,500 was reported in a warehouse 
in Oxalis, California, and a maternity colony of unspecified size was found roosting between walls 
and the roof of the warehouse at San Simeon (Dalquest, 1947a). A building in the Trans-Pecos 
region of western Texas also was used as a maternity roost (Yancey, 1997), as was an old cabin near 
Malheur Lake, Oregon and an attic at Eagle Lake in northeastern California (Bailey, 1936). A 
maternity colony numbering 1,600 has been reported in an abandoned church as far north as British 
Columbia (Milligan, 1993; Milligan and Brigham, 1993), where they also apparently roosted in a 
mobile home in the same region (Fenton et al., 1980). A colony at San Antonio, New Mexico (ele¬ 
vation 1,392 meters), roosted in a church roof and steeple together with Arizona myotis (M. occul- 
tus ), with a combined estimate of 1,800 bats of both species (Chung-MacCoubrey, 1999), and a 
maternity colony of 200 used the attic of a seminary at the higher elevation (2,042 meters) town of 
Montezuma, San Miguel County, New Mexico (Studier, 1968). About 2,000 females and young 
occupied a roost in the loft of a bam near Solano, California during summer, where high tempera¬ 
tures of 50°C were reached at upper parts of the roosting area during the day (Licht and Leitner, 
1967a). Extremes of heat in these roosts were evaded by behavioral thermoregulation and selection 
of appropriate microclimates within the roost when temperatures exceeded about 40°C (ambient 
temperatures above 43.5°C were lethal; Licht and Leitner, 1967a,b). 
Yuma myotis were found roosting in diurnal colonies in narrow crevices under multiple high¬ 
way bridges over the Rio Grande in southern New Mexico, including at least seven maternity 
colonies and nearly 14,000 individuals; roosting sites were at least 1.1 meters above ground, with 
most in bridges constmcted of timbers (Geluso and Mink, 2009). A colony of at least 250 roosted 
under a small concrete bridge near the Rio Grande at Bosque Del Apache National Wildlife Refuge 
in New Mexico (Chung-MacCoubrey, 1999). Bridges were found to serve as both maternity and 
night roosts in the central Sierra Nevada of California, where some colonies roosted behind metal 
signs posted at the bridges, 10 of 20 inspected bridges held summer colonies, and six were used as 
night roosts; the largest colonies at bridges held over 1,000 individuals (Pierson et al., 2001). Struc¬ 
tural features of bridges used by this species and roosting places beneath them have been described 
in detail elsewhere (Pierson et al., 1996b, 2001; Geluso and Mink, 2009). Use of a wooden bridge 
in the Bitterroot Valley of Montana by a maternity colony of several hundred was noted by Bailey 
(1936). 
Transient spring and autumn colonies in crevices of the Davis Dam on the Colorado River near 
Bullhead City, Arizona numbered as high as 10,000 bats in 1960 (Cockrum et al., 1996). The 
London Bridge at Lake Havasu, Arizona houses a maternity colony of several thousand individu¬ 
als, and a smaller colony roosts at Baseline Bridge over the lower Colorado River at Cibola, 
Arizona (Brown, 2013). 
Night Roosts: Yuma myotis will night-roost in deserted buildings, as described by multiple 
authors (for example, Cary, 1911; Warren, 1942; Dalquest and Ramage, 1946; Dalquest, 1947a,b; 
Easterla, 1973; Pierson et al., 1996b; Adam and Hayes, 2000). Maximum aggregations of 250 to 
450 individuals (primarily females and volant young) have been noted during summer in night 
roosts under two abandoned bridges over the Sacramento River in northern California, with indi¬ 
vidual bats showing fidelity to these night roosts from year-to-year (Pierson et al., 1996b). They 
also used bridges as night roosts in the Trans-Pecos region of western Texas (Yancey, 1997). Six¬ 
teen of 20 bridges inspected for night roosting in the central Sierra Nevada in and near Yosemite 
National Park were used as night roosts, mostly by Yuma myotis (Pierson et al., 2001). Albright 
(1959) reported this species to commonly night roost at a cave at Oregon Caves National Monu- 
