ABSTRACT 



One hundred and seventy-three abandoned mine workings (77 adits, 96 "shafts" and pits) 

 at 88 mine sites in southwestern Montana (Beaverhead, Madison, and Silver Bow counties) were 

 investigated for evidence of use by bats during 1997-1998. Of the mine workings, 40 (23.1%) 

 were partly or completely collapsed. Evidence of bat use was collected from 66 workings at 49 

 mine sites. Bat activity was detected with ultrasonic bat detectors or trapping at 61 workings of 

 45 mine sites. Bat guano (usually only one or a few droppings) was present at 5 additional mine 

 workings at 4 mine sites where there was no other evidence of bat use. No maternity sites were 

 found (although single lactating females were captured twice at one mine); the majority of used 

 workings were probably night roosts. Only one working was confirmed as a hibernaculum, but 

 several others may be so used. 



Sixty-four individuals represented by Western Small-footed Myotis (Myotis ciliolabrum). 

 Western Long-eared Myotis (M. evotis). Big Brown Bat (Eptesicus Juscus), and Townsend's 

 Big-eared Bat (Corynorhinus townsendii), were captured or observed at 1 7, 5, 2, and 3 mine 

 workings, respectively. Sex ratio of captured bats was extremely male biased. Most bat detector 

 results (at 47 of 50 workings with detections) were identified as unknown bat or unknown 

 Myotis, but species identifications were tentatively assigned to M. evotis at 10 workings, E. 

 fuscus at 12 workings, C. townsendii at 6 workings, and Lasionycteris noctivagansl Lasiurus 

 cinereus at 4 workings. 



Monitored mines at higher elevations were used less often than mines below 6000'. 

 Unobstructed mine workings were used more often than workings with partial obstructions, and 

 adits in both categories were used more often by bats than were shafts. The elevation 

 distributions of monitored adits and shafts were similar, and therefore not a factor confounding 

 the general elevation partem of use. Dominant vegetation at most (87%) of the monitored 

 workings was sagebrush shrubland. and was also not a confounding factor in the detected 

 patterns of mine use. Neither portal size nor the number of open portals at a mine site appeared 

 to affect use by bats. Proximity to water could not be accurately determined, but most workings 

 were < 2 km from known surface water, which is probably within the nightly foraging range of 

 most bats. 



Twelve mine workings were inspected internally for the presence of bats. Mines chosen 

 for entry were selected based on relative hazard and prior evidence of bat use. Bats (four total) 

 were found in three mines. Data loggers were installed in six mine workings to record over- 

 winter mine air temperature and relative humidity every six hours. Data logger results are not 

 included in this report, but will be provided as an addendum. Climate data taken at the time of 

 entry indicate most sites probably are too cold for maternity colonies. 



It is recommended that all open workings be considered as potential habitat for bats in 

 this area. None of the workings where bat activity was confirmed should be closed, although 

 monetary considerations could limit the number of workings modified to protect bats while 

 restricting access to humans. Instead, other protective and bat-friendly measures should be 

 considered, such as the installation of gates. Highest priority sites are those confirmed, or with 

 the potential, to be maternity and/or hibernation roosts. The current method for closing shafts 

 and other "vertical" workings (ground-level grating with 1x3 inch openings) effectively prohibits 

 access by bats. Replacement of fine-meshed grates with an alternative, bat-friendly design might 

 allow bats to use a number of these workings. 



