cave in summer, although cave temperature 

 tliroughout is 3.3 °C (Worthington 1991 ) making it 

 too cold for use as a maternity roost. 



As our data across a range of elevations show 

 (Table 2, Appendix 1 ), mines in westem Montana 

 generally provide relatively cold roost environ- 

 ments for bats regardless of season. Greatest use 

 of abandoned mines by bats in westem Montana 

 is for day/night roosts and hibemacula. Many 

 abandoned mines in southwestem Montana 

 present bats with a variety of summer microcli- 

 mates (Table 2) and are used briefly as night 

 roosts (Hendricks et al. 1 999), where meals are 

 digested in relative safety. However, hibemacula 

 are the best-documented roost climates in Mon- 

 tana, although data are usually point (single date) 

 samples, and bat species found hibernating often 

 are unidentified to species. Fortunately, the 

 exception is C. townsendii, because it is relatively 

 easy to identify, even when torpid and undis- 

 turbed. 



In Montana, C. townsendii use caves and mines 

 across a broad range of elevations for hibernation 

 roosts (Table 4). Torpid C townsendii have 



been found from November tlirough April in sites 

 where the respective ranges of temperature and 

 relative humidity are -1 .0-8.0 °C and 50-100% 

 (see also Table 2). Number of hibemating indi- 

 viduals at each of these sites (Table 4) was < 20, 

 although larger winter numbers have been re- 

 ported in appropriate winter roosts in the lower- 

 elevation plains of eastem Montana (Swenson 

 1 970), where few surveys have been conducted. 

 The data presented in Table 4 suggest that roosts 

 below 2000 m elevation may routinely support 

 larger winter aggregations of C townsendii. This 

 pattern could arise because arid landscapes often 

 favored by tliis species (Sherwin et al. 2000) are 

 found at lower elevations in the region, or because 

 maternity roosts are often < 20 km from hiber- 

 nacula (Humphrey and Kunz 1 976, Kunz and 

 Martin 1982,Dobkinetal. 1995) and are prob- 

 ably more abundant at lower elevations. Microcli- 

 mates for Montana hibemacula of C. townsendii 

 are similar to those reported in the literature from a 

 number of westem and midwestem states 

 (Pearson etal. 1952,Twente 1955,Twente 1960, 

 Humphrey and Kunz 1976, Center 1986, Pierson 

 et al. 1 99 1 , Webb et al. 1 996, Choate and 

 Anderson 1 997, Kuenzi et al. 1 999), with winter 



Table 4. Summary of point-sample (single date) microclimate data for Townsend's Big- 

 eared Bat {Corynorhinus townsendii) hibemacula in Montana. Temperature (T) and 

 relative humidity (RH) data were recorded near hibemating bats using a sling 

 psychrometer. 



^ 1) this study, 1998-1999; 2) Hendricks et al. 2000; 3) Hendricks 2000; 4) unpublished 

 data, 2000; 5) Madson and Hanson 1992. 



10 



