roost temperature typically ranging between -1 .5- 

 10.0 °C. However, in some California locations 

 roost temperature near torpid individuals may 

 reach 21.0-25.0 °C(Piersonetal. 1991, Webb et 

 al. 1 996), much wanner than for any Montana 

 hibemaculum. 



Management Implications: There are two 

 major approaches for assessing abandoned mines 

 for bats: external and internal surveys (Altenbach 

 1995.Navo 1995). During external surveys data 

 are gathered on the number and dimension of all 

 entrances (portals), airflow, outside air tempera- 

 ture, presence of standing water, and visual sign of 

 bats (carcasses, roosting bats, droppings); one 

 portal survey in spring, one in summer, and two in 

 fall are recommended (Navo 1995). Use of 

 electronic bat detectors can aid in portal surveys. 

 Internal surveys allow direct measurement of mine 

 tempjerature and relative humidit>', and also an 

 assessment of the extent of underground workings 

 and their configuration as well as e\idence of bats 

 at specific locations within the mine. Cold season 

 internal surveys can determine both summer and 

 winter use, whereas warm season surveys can 

 determine only summer use. 



Our analysis identified few mine characteristics 

 measurable from external surveys that are good 

 predictors of mine suitability for bats, with the 

 exception of obstructions across portals that inhibit 

 or preclude bat access (Hendricks et al. 1 999). 

 Mine temperature is an important feature for roost 

 selection by bats (Dwyer 1971. Humphrey 1975), 

 and relative humidity may also be important (Betts 

 1997). We found a significant negative relation- 

 ship betw een elevation and summer or winter mine 

 temperature (Figure 2). but not between elevation 

 and relative humidit>'; mines at higher elevation 

 were colder year round, but not necessarily less 

 humid. Mean mine temperature during both 

 summer and winter was highly correlated (Figure 

 3 ). indicating that temperature taken during one 

 season is a good predictor of temperature during 

 the other season in the same mine: this pattem was 

 also found for relative humidity. Nevertheless, 

 obtaining these measurements required going 



underground. 1- urthermore, we found consider- 

 able short-temi variation in temperature and/or 

 relative humidity in most of the mines we moni- 

 tored ( Apf)endix 1 ), making questionable the 

 characterization of their year-round climate from 

 data obtained during a single visit (Sherwin et al. 

 2000). If surveys are restricted to one or two 

 visits because of monetarj' or logistical limitations, 

 the potential for significant short-term variation 

 should be kept in mind when characterizing the 

 mine climates. 



We also found that mines with climates largely 

 unsuitable for use by bats may contain areas within 

 them that can be and are used (Table 2, Appendix 

 1 ). It is not possible to identify these internal 

 microsites from extemal surveys, with the possible 

 exception of the shallowest mines with workings 

 completely visible from the portal. Identification of 

 liibemacula, the most likely mine roosts to be used 

 over several continuous months in Montana, is 

 impossible from extemal survey alone. Further- 

 more, internal survey is the quickest and least 

 labor/time intensive method for determining mine 

 suitability for bats in all seasons (Pierson et al 

 1 999). We therefor suggest that, where safe, 

 internal survey is the preferred method for assess- 

 ing mine use and suitabilit>' for bats. Where mine 

 entry is impossible or unsafe, extemal survey at the 

 portal must suffice. In these cases it is critical that 

 surveys are conducted at the appropriate time. 

 Possible hibernation activitv' is detected best in fall 

 (September and October) when bats swarm at 

 their hibernation roosts. Matemit>' use of mines is 

 detected best in summer (July and August) when 

 females are pregnant or lactating. 



We recommend that all abandoned mines sched- 

 uled for reclamation on public lands receive 

 proper evaluation as bat habitat prior to closure, 

 whether by extemal or internal survey. Protocols 

 for mine evaluation are presented in the conserxa- 

 tion assessment and strategy for the Townsend's 

 Big-eared Bat, ( '. tow nsendii (V'xcrson et al. 

 1 999), as well as Altenbach ( 1 995 ) and Navo 

 ( 1 995). and are appropriate for all mine-dwelling 

 hat species in Montana. 



11 



