The information content of hornbill vocalizations is poorly understood and there are no detailed studies of the potential information content of hornbill vocalizations. Hornbills probably use information presented in their loud-calls to recognize individuals. The study presents both the first multivariate analysis of hornbill vocalizations and the first bioacoustic study of any Philippine hornbill species. I analyzed loud calls of two Philippine hornbill species, Rufous-headed Hornbill (Aceros waldeni) and the Visayan Hornbill (Penelopides panini panini). I found that loud-calls of both hornbill species contain individually specific characteristics. The acoustic variables describing the most variation among individual Visayan Hornbills were both spectral and temporal variables. Rufous-headed Hornbill individual calls were differentiated mainly by spectral variables. Frequency parameters in Rufous-headed Hornbill calls were significantly lower than those in Visayan Hornbills. The bioacoustic methods have a strong potential in conservation. The use of acoustic monitoring of individuals as a non-invasive marking technique could help to monitor hornbill individual life history and also to collect many biological data on these endangered Philippine hornbills that are currently lacking.
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