cxjnfused on the Deer lodge National Forest are the Fringed bat (Myotis 

 thysanodes) with the Northern long-eared bat {Myotis evotls) , and the 

 Yuma bat (Myotis yunanensis) , California myotis {Myotis 

 calif omicus) , and Little brown bat {Myotis lucifugus) oorplex. 



Ftelative density 



Relative density between sites and between habitats by different bat 

 species can be determined using ultra-sonic bat detectors. 

 Discussions of the various types of ultrasonic detectors, along with 

 their inherent strengths and weaknesses, can be found elsevdiere (see 

 Fentcn 1988, and Thomas and West 1989). One or two tunable 

 heterodyne detectors were used during this study. These detectors 

 can be tioned to a number of frequencies, but can only scan a narrow 

 band at one time. Detectors were normally set at 40 kHz during 

 surveys, as most bats in Montana can be detected at that frequency. 

 If a bat was heard long enough, an attempt was made to determine its 

 lowest detectable frequency, as several species, or groups of 

 species, can be identified using this characteristic. 



The intensity of the echolocation call differs between species, as 

 well as the frequency range of the call. This characteristic biases 

 relative density infomiation between species. Bats with intense 

 vocalizaticffis, such as Hoary bats {Lasiurus cinereus) or Big brown 

 bats {Eptesicus fuscus), are much more likely to be detected than 

 tlxDse with weaker vocalizations, such as Townsend's big-eared bat. 

 Myotis species fall between these extremes in intensity of their 



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