Effects of Interindividual Variation in Echolocation Calls on Identification of Big Brown and Silver-Haired Bats

Abstract

Identifying bat species from their calls is a common technique in studies of habitat use. I tested the hypotheses that significant interindividual intraspecific variation exists in the echolocation calls of bats as detected by frequency-divide ultrasonic detectors, and that such variation could greatly affect the accuracy of species identification. I restricted analysis to 2 species that have similar hut reportedly distinguishable calls. There was significant intraspecific variation in 6 variables for each species, and frequency distributions of the 2 species overlapped greatly for all 6 variables; hence, univariate analysis was ineffective at differentiating between species. The best of experienced human observers correctly identified the species for only 70% of 47 call sequences compared to >95% correct classification by discriminant function analysis. Alterations in current methodology can improve accuracy of identification and thus the value of habitat studies and management decisions that rely on such identification.