48 
PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, Supplement I 
wide. Maternity groups formed round, densely packed clusters of 35 to 81 adults and young in 
order to maintain high body temperatures to facilitate growth and development of young. No other 
species roosted nearby (Humphrey and Kunz, 1976). Females were usually not torpid and were 
alert (except during cold spells) in maternity colonies, which dispersed in late summer. One of the 
largest non-winter aggregations reported in recent times was observed in September 1976, when 
“several hundreds” were reported from “Stanton Cave” [Stanton’s Cave] in Grand Canyon (Suttkus 
et al., 1978:4). More than 1,000 individuals have been counted emerging from a maternity colony 
in an abandoned mine that taps into a geothermally heated cave in the mountains of western Col¬ 
orado (Siemers and Neubaum, 2015). 
Males were detected in surveys of mine tunnels in the Huachuca Mountains of southeastern 
Arizona during 1949-1951, where nearly every tunnel had Townsend’s big-eared bats, often in the 
same roosts used by Mexican long-tongued bats (Hoffmeister and Goodpaster, 1954). Males 
remain solitary or roost in very small groups, with an occasional few found among females in 
maternity colonies or in different parts of the same cave or mine (Howell, 1920a; Humphrey and 
Kunz, 1976; Kunz and Martin, 1982 and references therein; Pierson et al., 1991; Sherwin et al., 
2000). Bachelor roosts (containing only males and non-reproductive females) were found in about 
25% of 715 caves and min es surveyed in Utah, each housing one to seven individuals (Sherwin et 
al., 2000). During summer, males often roost solitarily near entrances of caves, mines, and build¬ 
ings, but small numbers can sometimes be found scattered elsewhere in the same roost (Humphrey 
and Kunz, 1976, Sherwin et al., 2000). Males in some mines can show fairly deep daily torpor dur¬ 
ing summer, particularly at mid-elevations in mountainous region (Grinnell and Swarth, 1913; 
Dalquest, 1947a). 
Warm Season Roosts in Structures other than Caves and Mines: Although caves and aban¬ 
doned mines are the most important roosting habitat for this species, they also have been docu¬ 
mented using buildings, tree hollows (Fellers and Pierson, 2002; Mazurek, 2004), and spaces under 
boulders or in crevices in rock outcroppings. The latter was reported in ponderosa pine forests in 
northwestern Arizona (Herder and Jackson, 2000), and two adult males radio tracked to roosts for 
six to 15 days in the Jemez Mountains of New Mexico roosted solitarily in three separate, small 
rock crevices low on cliff walls (Bogan et al., 1998). In western Nevada, radio-tracked males and 
non-reproductive females frequently roosted solitarily in such crevices rather than nearby caves or 
mines, switching roosts daily (Ives, 2015). 
Townsend’s big-eared bats will roost in buildings throughout their range in the western Unit¬ 
ed States. As examples, Cryan (1997) reported a maternity colony of about 40 females and young 
in the attic of an abandoned building in South Dakota; a maternity colony of 300 adult females was 
observed in an attic in eastern Oregon (Betts, 2010); a lone roosting female was found in an attic 
in Utah (Hardy, 1941); and a colony of 12 was observed during September in an abandoned farm 
building in northeastern Montana (Swenson and Shanks, 1979). In California, Dalquest (1947a) 
described a maternity colony of about 75 bats, most in a tight cluster, in the attic of a mission in 
Alameda County, a smaller maternity colony in an attic of a winery in Napa County, and multiple 
buildings housing isolated males. A maternity colony of 130-145 adults and volant young used a 
two story adobe ranch building on Santa Cruz Island, California during summer 1992, where a larg¬ 
er colony of about 300 was known from the attic of an old building on the island during the 1930s 
and 1940s (von Bloeker, 1967; Brown et al., 1994). The only known roosting sites of this species 
in coastal areas of California are in old buildings, a bridge, and large basal hollows in trees (Gell- 
man and Zielinski, 1996; Pierson et al., 1999; Fellers and Pierson, 2002; Mazurek, 2004). Bridges 
were found to house diurnal roosts of these bats in the central Sierra Nevada of California (Pierson 
et al., 2001). In western Colorado, a maternity colony of Townsend’s big-eared bats numbering as 
