1995, Bogan et al. 1996, Vonhof and Barclay 1996, Kalcounis and Brigham 1998, Ormsbee and 

 McComb 1998, Rabe et al. 1998). 



The degree to which any of the examined workings are used by bats as hibernacula is 

 largely unknown. It can be very difficult to determine the importance of a mine as a 

 hibernaculum based solely on external surveys unless a visit happens to coincide with bats 

 returning to the site to overwinter. Internal temperature regimes, mean annual surface 

 temperatures, and mine complexity may be good predictors of such use in some areas (e.g., 

 Dwyer 1971, Turtle and Taylor 1994), and such information could help in judging the necessity 

 for future internal surveys at selected sites. Some aspects of internal temperature and relative 

 humidity regimes of mines in southwestern Montana may be inferred from data obtained through 

 the data loggers in place from September 1998 to August 1999. These records will be supplied 

 in a supplemental report following instrument retrieval and data analysis. 



The Hendricks is currently the only mine in the study area that is known to be a 

 hibernaculum; one M. ciliolabrum and one E.fuscus were found hibernating in the mine on 4 

 December 1998 (Tables 2 and 4, D. Kampwerth pers. comm). This mine is on land formerly 

 owned by the BLM but now under jurisdiction of Bannock State Park. It seems probable, 

 however, that several other mine hibernacula are present on BLM lands in the inventory area. 

 The four bat species captured during this study have been documented over-wintering in mines 

 or caves elsewhere in Montana (Swenson 1970, Swenson and Shanks 1979, Hendricks et al. 

 2000), Idaho (Genter 1986), and Wyoming (Priday and Luce 1997). Two studies where M 

 ciliolabrum and C. townsendii co-occur (Genter 1986, Kuenzi et al 1999) indicate that the 

 former species may occupy slightly colder hibernacula. 



Mine Selection 



Results of this inventory showed that bat activity at monitored abandoned mines was not 

 uniform across the study area. On a landscape scale, higher-elevation workings (> 6000') were 

 used less frequently than workings at lower elevations (Fig. 2). Why this should be so is not 

 entirely clear, especially given that most used workings appeared to be night roosts. In regional 

 and local studies, reproductive females favor lower elevations, presumably because of the more 

 favorable climate conditions in which to raise young (Thomas 1988, Nagorsen and Brigham 

 1993, Storz and Williams 1996) Their absence from higher-elevation areas still would not 

 explain why mine workings were visited less frequently by males and non-reproductive females. 

 Perhaps population densities of bats at higher elevations in this region are extremely low for 

 reasons other than the availability of underground roosts. 



On a more local scale, unobstructed workings were more likely to be used, although the 

 difference for adits was very slight. More surprisingly, adits, whether obstructed or not, were 

 more likely to be used than shafts (Fig. 3). Why partially obstructed workings might deter bat 

 use is seemingly self-evident, through inhibiting access. The differential use of adits and shafts 

 is less easily explained. I am not aware of other studies showing a preference for one kind of 

 working over another, either within a suite of bat species, or by any particular species of bat. It 

 is possible that horizontal adits may better hold warm air overnight than vertical shafts, and that 

 bats seek warmer places to night roost. In Arizona it has been shown that night roosting by 

 Pallid Bats (Antrozoas pallidus) in horizontally oriented grottos typically began when external 

 air temperature cooled below that of the warmer internal air (O'Shea and Vaughan 1977). It is 

 also possible that some species of bats prefer to enter horizontal workings. This pattern merits 

 additional study. 



