Seeing the species through the trees: Using Random Forest classification trees to identify species‐specific whistle types

Acoustic identification of delphinid species is hampered by high variability in whistle characteristics. It is possible that not every whistle contains species‐specific information and that there are “species‐specific” whistle types. Random forest analysis was used to examine whistles of 8 species recorded in the eastern tropical Pacific Ocean (Delphinus species, Globicephala macrorhynchus, Pseudorca crassidens, Stenella attenuata, S. coeruleoalba, S. longirostris, Steno bredanensis, Tursiops truncatus). Fifty‐one variables were measured from 2176 whistles. The number of trees within a random forest that “voted” for the predicted species was used as a measure of the strength of classification. A whistle was considered strongly classified if the predicted species received at least 40% of the votes, even if the prediction was incorrect. The percent of whistles that were strongly classified ranged from 33% (S. longirostris) to 73% (G. macrorhynchus). Overall, 62% of strong whistles were correctly classified, ranging from 22% (S. longirostris) to 87% (P. crassidens). Overall correct classification for weakly classified whistles was 33% and ranged from 17% (Delphinus spp. and G. macrorhynchus) to 55% (S. bredanensis). Results suggest that while there may be “species‐specific” whistle types, the distinctiveness of these whistles and the frequency with which they are produced varies among species.