O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
89 
“Management Practices and Concerns” below). A maximum life span of about 15 years has been 
reported from banding studies (Brown et al., 1993a,b). 
Population Trend: Counts at five colonies in Arizona were analyzed for temporal trends but 
none was detected (Ellison et al., 2003). Internal counts at one mine were found to vary greatly 
across multiple visits both within and among seasons, showing the difficulties of attempting to 
determine trends in count data for this species (Ellison et al., 2003). Emergence counts of these bats 
also can be influenced by strong negative effects of observation method (for example, human 
observers or video recording), the presence of other bat species in the same roost, bright moonlight, 
very cold weather, and wind (Brown, 2013). 
Historical accounts suggest much greater past abundance of California leaf-nosed bats than 
known at present. For example, Howell (1920a: 172), remarked that of the many caves along the 
rocky coastline of the Salton Sea “nearly all are tenanted by colonies of this bat—from a score to 
two-hundred individuals to a colony.” These and other historically known colony sites are appar¬ 
ently now abandoned, and other more recently documented colonies have been abandoned or have 
declined (Brown, 2013). As examples, Brown and Berry (1991) reported the sealing of a materni¬ 
ty colony site in California during open pit mining operations, as well as the decline of a winter 
roost population that was stable at 150 animals in 1976 to 11 bats by 1990. This reduction was 
attributed to destruction of desert wash vegetation as foraging habitat and disturbance during 
resumed mining (Brown et al., 1993a,b; Brown, 1995). Constantine (1998a) reported the absence 
of this species from two caves in southern California that had housed low numbers in the 1940s 
(one cave had been destroyed, the other had signs of use as a “party site” and was surrounded by 
housing developments; Brown and Berry, 2005:14). A mine shaft used by a colony in Nevada was 
flooded by the impoundment of the Colorado River to form Lake Mead (O’Farrell, 1970), with 
unknown population consequences, and a mine tunnel in Arizona that formerly housed these bats 
was sealed shut (Brown, 2013). 
Recent multi-agency sponsored monitoring of California leaf-nosed bat colonies along the 
Lower Colorado River from Laughlin, Nevada to near Yuma, Arizona began in 2002, and was ini¬ 
tially based on emergence counts at ten mine complexes (Brown, 2013). Counts were made through 
2010, with 6 of the mines also having prior data available and three more mines added after 2010. 
Counts at all but one mine showed year-to-year variability but no discernible trends (Brown, 2013). 
Counts at one ungated mine on the Imperial National Wildlife Refuge in Arizona used as a mater¬ 
nity colony declined from over 700 bats in spring 2001 to less than 100 in spring 2013, likely due 
to visitor disturbance (Brown, 2013). Emergence counts during winter at a long-occupied and now 
gated mine in California have appeared stable at over 2,000 bats during monitoring from 2001 to 
2013 (Brown, 2013). 
Population Genetics: Estimates of mean heterozygosity based on allozyme variation at 17 
loci in a sample of 45 individuals from a mine in Pima County Arizona were quite low (0.03), indi¬ 
cating low genetic variability in that sample (Straney et al., 1976). 
Management Practices and Concerns. — Creation and abandonment of min es in the 
western United States over the last two centuries could have initially added roosting habitat for 
these and other cavemicolous bats. However, some of these possible gains are subsequently lost as 
abandoned mines begin to naturally fill or are closed for safety reasons. California leaf-nosed bats 
will roost in mines fitted with bat-compatible gates and, as noted in the following examples, prop¬ 
erly designed and installed gates are an effective way of protecting this species from human 
disturbance. The National Park Service has used bat-compatible closure methods at abandoned 
mines occupied by this species at Lake Mead National Recreation Area and Joshua Tree National 
Park (Burghardt, 2000). An abandoned mine on Bureau of Land Management property in south- 
