O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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(Commissaris, 1961). This species will also roost in abandoned mine tunnels. A maternity colony 
of about 100 adult females and juveniles occupied two nearby mine tunnels, and about 25 used a 
third tunnel, all in lower Sonoran desert at about 800 meters elevation and 50 kilometers from 
forested habitat in Mohave County, Arizona during 1960-1962 (Cockrum and Musgrove, 1964a). 
The main roost was subsequently destroyed due to road construction (Cockrum et al., 1996). Three 
adult females were radio tracked to roosts at Grand Staircase-Escalante National Monuments in 
southern Utah during 2004; all were found using rock crevices in the top of a high sandstone cliff 
in a small box canyon in pinon-juniper woodland, where estimated colony size was at least 15 bats 
(Siders and Jolley, 2009). 
Allen’s big-eared bats will form maternity colonies in tree snags. Rabe et al. (1998a) used 
radio telemetry to determine roosting habits of 16 adult females during the maternity season in pon- 
derosa pine forests of the Coconino National Forest in northern Arizona. All roosted in colonies 
under exfoliating bark in ponderosa pine snags. Eleven of these roosts that housed maternity 
colonies were found 11-14 years later by Solvesky and Chambers (2009): only one held a colony 
(eight bats), five snags were standing but had no exfoliating bark and thus seemed unsuitable as 
roosts, and the remainder had fallen or were presumed cut for firewood. The total number of roosts 
located by both Solvesky and Chambers (2009) and Rabe et al. (1998a) was 27. All but one were 
under exfoliating bark of ponderosa pine snags attached at the upper horizontal ends; one roost was 
in a vertical crevice in a building (Solvesky and Chambers, 2009). Maternity colony sizes based on 
emergence counts averaged 11 individuals (range two to 21), with each of 14 radio-tagged preg¬ 
nant or lactating females using one to three different roosts in a 10-day tracking period; two roosts 
of tagged males were in vertical sandstone cliffs at lower elevations than maternity roosts 
(Solvesky and Chambers, 2009). Maternity roost trees were closer to roads, taller, and in forest 
stands with more downed debris and greater canopy closure than comparison snags chosen at ran¬ 
dom bearings and distances from capture sites. Solvesky and Chambers (2009) speculated that for¬ 
est roads might be used as flight corridors, that taller snags provide more exfoliating bark, that 
canopy closure may decrease cooling and winds (which could increase chances of bark sloughing), 
and that greater debris on the ground may be residual in areas where the bats might show higher 
fidelity because of formerly high snag densities. Six female Allen’s big-eared bats radio tracked in 
east-central Arizona ponderosa pine forest roosted in three ponderosa pine snags, one Douglas fir 
snag, and one rock crevice, with mean colony sizes of 7 bats observed in exit counts (range up to 
15; Saunders, 2015). 
Allen’s big-eared bats have rarely been reported roosting in buildings. A maternity roost with 
an unspecified number of bats was located in a vertical crevice in a residential building in north¬ 
ern Arizona (Solvesky and Chambers, 2009). A single male was reported roosting in the eaves of 
a house in Arizona (Cockrum and Musgrove, 1964a), and a single adult female was observed hang¬ 
ing from a rafter of a picnic shelter in western Colorado (Adams and Lambeth, 2015). 
Roosting habits of male Allen’s big-eared bats are poorly known. Two males in northern Ari¬ 
zona were radio tracked to two roosts in vertical sandstone cliff faces, but numbers of roost mates 
were not known (Solvesky and Chambers, 2009). Curiously, 16 were netted over a small pond in 
Gila County, Arizona, on three summer nights and all were males (Hayward and Johnson, 1961), 
perhaps suggesting the existence of nearby bachelor roosts or colonies. 
Population Ecology. — Litter Size, Natality, and Female Reproduction: One adult 
female sampled in Utah contained a single fetus (Black, 1970), as did three females sampled in 
New Mexico (Jones, 1961; Findley et al., 1975). Each of 11 adult females captured at a maternity 
colony in Mohave County, Arizona during summer 1961 were lactating (Cockrum and Musgrove, 
1964a). Natality rates of bats captured over water also are high based on the limited data available. 
