from the portal on 4 December (D Kampwerth, pers. comm ), near one of the temperature and 

 humidity dataloggers. The large amount of guano throughout the passages of this mine suggest 

 greater use by bats than revealed in this study In other mines, one Townsend's Big-eared Bat 

 (Corynorhinus townsendh) was observed in the Plainview B on 1 1 July, and one fresh dead 

 Western Small-footed Myotis was found in the Unnamed Gold deposit #2 on 3 September 



DISCUSSION 



General 



The most abundant bat species using the abandoned mines surveyed in the study area 

 (Table 1) is probably the Western Small-footed Myotis (Myotis ciliolabrum), 49 (78.1%) of the 

 64 bats captured or identified by sight were this species (Table 2) This species was captured at 

 17 workings, over three-fold more than for any other species The Western Long-eared Myotis 

 (M. evotis) appears to be the second most abundant bat using the mines, comprising another 

 14. 1% (n = 9) of the total captured This species was captured at 5 mine workings and 

 tentatively identified with bat detectors at another 10 (Tables 2 and 3). These two species 

 combined probably also comprised the majority of unknown bat and Myotis species determined 

 on the bat detector recordings (Table 3) Both species are widespread in arid-land and forested 

 habitats of the western United States (van Zyll de Jong 1985, Nagorsen and Brigham 1993, Ports 

 and Bradley 1996, Szewczak et al 1998, Kuenzi et al. 1999). 



Townsend's Big-eared Bat (Corynorhinus townsendii), a BLM Special Status species in 

 Montana, was captured or sight-identified at 3 workings (Table 2), and tentatively determined at 

 another 3-6 workings using ultrasound detectors (Table 3) These encounters occurred in seven 

 townships, suggesting a broad geographical distribution at a low-level of abundance This 

 species also is routinely encountered using mines and caves in arid habitats (Humphrey and 

 Kunz 1976, van Zyll de Jong 1985, Nagorsen and Brigham 1993, Ports and Bradley 1996, 

 Szewczak et al 1998, Kuenzi et al 1999) The Big Brown Bat (Eptesicusfuscus) was the fourth 

 species captured (at 1 working and observed in another), and was tentatively identified with 

 ultrasound detectors at 10 additional workings This species is widespread over much of North 

 America (van Zyll de Jong 1985, Nagorsen and Brigham 1993) The final two species. Silver- 

 haired Bat (Lasionyctens noctivagans) and Hoary Bat (Lasiurus cmereus), were tentatively 

 identified only with bat detectors at 4 mine workings Both species rarely use mines and caves 

 for roosts (van Zyll de Jong 1985, Nagorsen and Brigham 1993), so their presence at mine 

 workings is likely a reflection of their foraging activity near these sites 



Bat activity in the inventory area was widespread during 1997-1998 However, intensity 

 of activity was relatively low at most sites, suggesting that the majority of used abandoned mine 

 workings served as night and/or day roosts. This does not mean that the mines are not important 

 for the bat populations of the survey area. Low population densities of bats could easilv account 

 for the relatively low activity at many workings, and sites in which to rest between foraging 

 forays remain important habitat components for bats 



None of the mine workings appeared to serve as a maternity roost, although this 

 conclusion is based on circumstantial evidence Few female bats were captured (Table 2), and 

 mine air temperatures were likely too cool for maternity sites (see discussion in Betts 1997) 

 Instead, most females raising developing young probably were using natural cavities in trees and 

 rock outcrops, where warmer temperatures occur (e.g., Humphrey and Kunz 1976, Dobkin et al 



