There are factors that confound the differential use of adits and shafts, however, making 

 tentative the conclusions drawn from that pattern First, obstructions at shafts, especially grates, 

 may be more effective barriers to bats, even though there may be a missing door in the grate, or 

 there is some sloughing below the edges that might allow access near ground-level Obstructions 

 at adits often include gates, cable netting, partially open wooden doors or collapsed headframes, 

 etc with spaces allowing the passage of bats Therefore, not all partial obstructions are equal, 

 and those usually associated with shafts appear to be more effective in excluding bats Second, 

 shafts may be more likely to be obstructed by debris falling from the ground surface and 

 accumulating in passages beyond the portal, as a result of their morphology Because most 

 workings (many adits as well as all shafts except two inclines) were not explored internally, there 

 is no way of knowing what conditions they offered to bats. This is probably the most important 

 shortcoming in attempting to develop external criteria for predicting mine suitability to bats, 

 surface conditions may be completely unrelated to conditions underground 



Access to water is an important component in the spatial environment of bats that affects 

 where they are active This could not be realistically measured during this inventory, as there are 

 many unmapped sources of surface water in most areas and at many times during an active 

 season However, most monitored workings were within 2 km of known surface streams or 

 stock ponds, well within the nightly foraging distance from roosts of some bat species (e.g., Wai- 

 Ping and Fenton 1989, Dobkin et al 1995). Furthermore, water is sometimes available 

 underground. At least 4 (25%) of the workings explored underground in 1998 had significant 

 pools of standing water within them. Without access to all workings (including those on private 

 land), proximity to water at any mine is speculative but is unlikely to be a significant factor 

 influencing mine use in this study area 



Some potential confounding variables that could influence the detected patterns can be 

 eliminated The majority (87%) of workings was in sagebrush habitat, so vegetation cover type 

 probably had a minor influence at most on which mine workings were used Also, the samples 

 of monitored adits and shafts were distributed similarly by elevation (Fig 1), so their relative 

 distributions across an elevation gradient had little influence on the preference shown for lower- 

 elevation mines, if indeed adits really are favored by bats in this region (see Fig. 3). 



Neither portal size nor the number of potentially suitable portals at a mine site affected 

 the pattern of mine use by bats Results of the portal size analysis could be biased for reasons 

 previously addressed (not all partial obstructions can be equally by-passed by bats), but the 

 distribution of grated shafts was roughly equal in the used and unused groups However, number 

 of portals at a mine site was classified into only two categories, one and more than one. With a 

 larger sample containing multiple portals per mine, a different pattern may appear Also, 

 distance between portals needs to be measured metrically, rather than classified by mine name 

 To do this analysis properly, it is necessary to include mine workings on private lands, unless 

 study areas are kept smaller than that of this inventory, and where access to all mines can be 

 assured 



MANAGEMENT CONSIDERATIONS 



Mine use by bats and nunc climate 



It is desirable to gather long-term climate data, using electronic data loggers, from a 

 variety of mines used by bats as maternity, hibernation, and/or night roosts in Montana These 



