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

Abstract

Birds of the same genus often share similar call repertoires, the aim of this paper is to find species-specific and common acoustic features across species. This can be a useful tool for identification purposes and for studying intra-interspecific communication. Similar flight call (tsip) in two closely related species (Anthus pratensis, Anthus spinoletta) were studied to find characteristics, that allows to discriminate the two species with acoustic means. 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 find whether these common call types show different degrees of similarity. Discriminant function analysis correctly classified 98.4% of A. pratensis and A. spinoletta flight calls. Three acoustic parameters showed the highest discrimination power: the frequency modulations, the maximum frequency value and the minimum frequency value of the peak frequency contour. Using these three values I proposed a simpler procedure for recognizing these two species, that allowed a correct classification of 96% of calls.The three call types of the four Anthus species were studied using cross correlation among spectrogram contours. Alarm calls of the four species showed stronger similarity, while the other call types were more distinctive, with soft call seeming to have a lower similarity between species and hence a higher distinctive power. These results suggest the hypothesis that alarm call is similar, because it retains features of a common ancestor easing heterospecific communication, while the other calls showed decreasing similarity and more species-specific features.