INTRODUCTION 



Because bats spend much of their h\es in roosts 

 (Kunz 1 982), knowledge of tlieir roosting require- 

 ments provides important life-liistory information 

 for understanding habitat use and seasonal pres- 

 ence of most species. Furthermore, suitable 

 summer and winter roosts may limit local and 

 regional distribution and relative abundance of 

 many temperate-zone bats (Humphrey 1 975, 

 Dobkin et al. 1 995), especially cave-dwelling 

 taxa. Thus conservation and protection of roosts 

 are critical long-tenn management activities for the 

 perpetuation of many North American bat species 

 (Sheffield etal. 1992). 



Bat populations in many natural caves have 

 declined or disappeared because of a variety of 

 human-induced disturbances (LaVal and LaVal 

 1 980. Richter et al. 1 993. Tuttle and Taylor 

 1 994). Abandoned and undisturbed mines now 

 serve as principle summer and winter roosts for 

 many cave-dwelling species (Tuttle and Taylor 

 1 994) because mines offer a variety of subterra- 

 nean microclimates similar to tliose present in 

 natural ca\es (Tuttle and Stevenson 1978). 

 Concern about the status of North American bat 

 populations increased dramatically in recent 

 decades (Pierson 1 998) when it was recognized 

 that significant numbers of abandoned mines were 

 being barricaded, backfilled, and blasted shut for 

 safety and hability reasons, without prior biological 

 survey to determine their significance for roosting 

 bats. 



We conducted a sur\'ey of abandoned mines on 

 BLM lands in southwestem Montana during the 

 summers of 1 997 and 1 998 (Hendricks et al . 

 1 999) to assess and characterize their use by bats 

 prior to potential reclamation activity-. We antici- 

 pated that our work would help managers identity- 

 sites currenth' used b>- bats, and that the infomia- 

 tion characterizing used abandoned mines might 

 guide future mine sur\ey and reclamation activity-. 

 We gathered long-term climate data from used 

 abandoned mines because roost climate is a major 

 influence on roost site use. Roost environment 



descriptions (especially temperature and relative 

 humidity at roost microsites) are ver\' limited for 

 bats in Montana, and most axailable data pertain 

 to roosts in caves ( Worthington 1 99 1 . Madson 

 and Hanson 1992, Hendricks 2000, Hendricks et 

 al. 2000). 



For each mine inspected internally in 1 998 and 



considered safe for reentry we placed electronic 

 data loggers to record daily mine temperature and 

 relative humidity over a 6- 1 2 month period. Our 

 objectives for this phase of the study were to: 1 ) 

 document daily mine ambient temp^erature and 

 relative humidity during winter and summer, 

 especially at underground microsites where we 

 found evidence of bat use, 2) determine the 

 seasons when mines were used for roosting, and 

 identify the bat species using the mines, and 3 ) 

 determine mine characteristics documented from 

 external sur\'e>'s that might be useful for identifying 

 underground environments that arc suitable for bat 

 roosts in abandoned mines. Of special interest 

 were mines used by Townsend's Big-eared Bat 

 {Corynorhinii.s townsendii) because this bat is a 

 Montana animal species of special concem, a 

 Montana BLM Special Status species, and a 

 species of high conservation concem throughout 

 its range (Pierson et al. 1991, Pierson etal. 1999, 

 Sherwin etal. 2000). 



METHODS 



We concentrated our study on ten mines between 

 45°10' N and 47° 16' N latitudes in southwestem 

 Montana (Figure 1 ). six mines in Bea\erhead. 

 Madison, and Silver Bow counties, supplemented 

 with four mines in Jefferson and Lake counties 

 known or suspected to be used by Townsend's 

 Big-eared Bat. Elevation of mines ranged from 

 853 m to 2249 m (Table 1 ). Mines used by bats 

 were identified first from historical records or by 

 external inspection during summer, and through 

 use of electronic bat detectors (ANABAT II, 

 Titley Electronics. Ballina, Australia) and mist-net 

 or harp trap sampling at portals. 



