Potential for the use of vocal individuality as a conservation research tool in two threatened Philippine hornbill species, the Visayan Hornbill and the Rufous-headed Hornbill

Abstract

This study presents the first multivariate analysis of hornbill vocalizations and the first bioacoustic study of any Philippine hornbill species. We analyzed loud calls of two Philippine hornbill species, the Rufous-headed Hornbill Aceros waldeni and the Visayan Hornbill Penelopides panini panini, to assess the possibility for their use in individual identification.

Our study showed that individuals of the two studied hornbill species can be identified on the basis of their loud calls, which means that these calls potentially contain information about the caller. Discriminant analysis classified 89% of individual Rufous-headed Hornbills and 90% of individual Visayan Hornbills correctly. The acoustic variables describing the most variation among individual Visayan Hornbills were spectral variables (second amplitude peak) and temporal variables (location of the maximum amplitude and call duration). The calls of individual Rufous-headed Hornbill were differentiated mainly by spectral variables (the fundamental and the first harmonic frequency, and additionally the upper quartile of the frequency range). Frequency parameters in Rufous-headed Hornbill calls were significantly lower than those in Visayan Hornbills. The use of acoustic monitoring of individuals as a non-invasive marking technique could help to monitor hornbill individual life history and to improve census data using capture-mark-recapture technique.