before dusk facing over water bodies or meadows, out over cliff faces, under or near bridges, or 

 down forest corridors and left in place overnight. An attempt was made to set out four or five 

 detector units each night. Recorded calls were analyzed on an IBM compatible PC using 

 ANABAT II zero-crossings analysis interface module (ZCAIM) and software. 



Assignment of vocalizations to a particular species of bat was achieved by matching 

 time-frequency structure of field recordings with a reference set of calls obtained from captured 

 individuals and published descriptions of vocalizations (e.g., Fenton et al. 1983, O'Farrell 1997). 

 However, bat species can show significant variation in call structure (Betts 1998, Barclay 1999), 

 and we did not actively track and record flying bats (O'Farrell et al. 1999) to maximize quality 

 and quantity of diagnostic sequences. Furthermore, some units recorded bats flying near 

 potential roosts, such as cliffs or bridge structures. Roost-exit calls and calls in high 

 environmental clutter tend to be fragmentary, lacking diagnostic features necessary for species 

 identification (O'Farrell 1999). Therefore, all species-level identifications based on recorded 

 vocalizations are considered tentative where made in this study 



Mvotis designations (as a group) were assigned to recordings with vocalizations of short 

 duration (< 3 msec) with a relatively linear, perpendicular call pattern. Where call sequences 

 were assigned toM evotis the sweep pattern ranged from a maximum 75 kFIz to a minimum of 

 30 kHz. Otherwise all were classified Myotis species. Calls with a bilinear (extreme curvilinear) 

 pattern were tentatively assigned to a non-Myotis species or classified as unknown bat. Passes 

 with call fragments were also designated unknown bat if no associated calls allowed finer 

 resolution. Bilinear call sequences were assigned to Eptesicusfuscus if a continuous frequency 

 tail fell within the range of 33-28 kHz with duration of the narrow band component of 1-3 msec, 

 and the maximum frequency extended to 45-50 kHz This could result in confusion with 

 Lasionycteris noctivagans (Betts 1998) because of significant overlap in call structure. 

 Maximum frequency of the latter species is about 40 kHz with a narrow band component lasting 

 3-5 msec, and calls with these characteristics were assigned to this species. However, in the 

 majority of cases these two species were not distinguished by the recorded calls. 



Number of "passes" (defined here as a distinct vocalization with at least a 1 sec gap 

 between prior and following vocalizations) was recorded as a measure of relative activity at each 

 site. At one site equipment malfunctioned prematurely, and at another site with recorded activity 

 the recorder malfunctioned during the night Therefore, relative activity as presented here is 

 useful primarily as an index with variable degrees of error. 



Capture of bats was attempted using 50-denier mist nets of various lengths (most often 

 2.8 and 6 m) and set in a variety of arrays across and along water bodies at two sites Nets 

 typically were operated for 2.0-2.5 hours (dusk until 21:30). Captured bats were identified with 

 aid of keys in van Zyll de Jong (1985) or Nagorsen and Brigham (1993). Individuals were 

 sexed, aged, measured (forearm, weight), reproductive status noted, then released. 



The undersides of all bridges spanning the Gibbon River (n = 5, including one just 

 outside the primary study area) and a section of elevated road on a wooden structure at a thermal 

 site were inspected for evidence of use by bats. Areas most likely to provide roosting sites 

 included steel I-beam girders near any cross structure, and the spaces between longitudinal spans 

 and pilings. Bat sign most often included accumulated droppings (easily distinguishable from 

 rodent droppings) and sometimes staining of surfaces above potential roosting sites. 



A visit was made to one thermal area off of the highway to inspect the undersides of 

 boulders for roosting bats or evidence of roosting activity (presence of bat droppings). This 



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