VOCAL SIMILARITY AND DIFFERENCES IN FOUR SPECIES OF THE GENUSANTHUS: ACOUSTIC FEATURE ANALYSIS OF SOME COMMON CALLS

Abstract

Similar flight call (tsip) of two closely related species (Anthus pratensis, Anthus spinoletta) showed species-specific characteristics, that allows to discriminate the two species only with acoustic means. Discriminant function analysis was able to correctly classify 98,4% of the recordings. Three acoustic parameters showed the highest power in the discrimination process: the frequency modulations of the call, the maximum frequency value and the minimum frequency value of the peak frequency contour. Using these three values I proposed a simple method for recognizing these two species, that allowed a correct classification of 96% of recordings. Three different call types (tsip, soft and alarm) of four species of the genus Anthus (A. pratensis, A. spinoletta, A. petrosus, A. cervinus) were also studied to investigate their acoustic similarity and difference. Alarm calls of the four species showed a very strong similarity, while the other two call types were more distinctive showing a much lower similarity, with soft call seeming to have a lower similarity between species and hence a higher distinctive power. These results supported the hypothesis that alarm call is similar, because it retains features of a common ancestor and may ease heterospecific communication, while the other two call types (tsip and soft) showed a decreasing similarity and more species-specific features. Integrative taxonomy is commonly used in phylogenetic studies and besides genetic and morphological information, acoustic data play a major role in taxonomic designation of birds. The song of passerines was extensively investigated in phylogenetic comparative studies, but the data reported in this paper suggest that also the comparisons of call repertoires in closely related species may be a useful tool for taxonomic studies.