Acoustic species identification of shrews: Twittering calls for monitoring

The acoustic signals of shrews (Soricidae) are largely understudied. As shrews are very vocal animals it may be feasible to use acoustic methods in field studies to assess ecological and behavioral data. In this study, we present the first detailed analysis of the twittering calls of six Central European shrew species (Sorex minutus, Sorex araneus, Neomys fodiens, Neomys anomalus, Crocidura russula and Crocidura leucodon). The analysis is based on over 6000 recorded calls from 121 individuals. Our results indicate that there is a large inter-individual variance and a large inter-specific overlap in the acoustic parameters of the calls. Each species uses a large spectral variety of calls without clear species specific call types. A species identification using the Support Vector Machine method on six species shows 66.2% accuracy; however, a pairwise comparison indicates accuracy between 68.5 and 97.3%. We propose to use acoustic monitoring of shrews in comparative studies to estimate the overall shrew activity. Moreover we suggest using the acoustic identification method in areas with few shrew species where the accuracy of the technique can be eligible.