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

SummaryThis 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.

Description and comparison of Philippine hornbill (Bucerotidae) vocalizations

“…Vocalisations of hornbills were found to reveal information on the individual (Policht et al 2009). Tarictic hornbills are the smallest amongst the hornbills and they have narrow casques (Kennedy et al 2000, Policht et al 2009). They also emit relatively higher frequencies compared to those of Buceros, Rhyticeros and Rhabdotorrhiunus .…”

“…The Papuan hornbill ( Rhyticeros plicatus (J.R. Forster, 1781)) was also incorporated in the study since it was formerly a subspecies of R. leucocephalus . For added comparison, the vocalisations of the Rufous-headed hornbill ( Rhabdotorrhinus waldeni (Sharpe, 1877), Mindanao hornbill ( Penelopides affinis Tweeddale, 1877) and Samar hornbill ( Penelopides samarensis Steere, 1890) were obtained from Policht et al (2009), Xeno-canto and Avocet, respectively.…”

“…The resounding vocalisations of hornbills aids their communication interaction with conspecifics and sympatrics in dense forest habitats, defence, territory and threat (Haimoff 2008, Poonswad et al 2013, Policht et al 2009), but there are few studies on their bioacoustics (Kemp 1998, Gonzalez 2012). However, bioacoustic analysis of the hornbills' calls has remained insufficiently studied despite its potential to provide valuable information to understanding communication and evolution as shown by Oba (1998).…”

An acoustic system for the individual recognition of insects

“…Nonincidental sounds have evolved to be species-specific, and have been used to detect and identify animal species for many years. Many animal calls can also be individual-specific, including those of fish (Crawford et al, 1997), amphibians (Bee et al, 2001), birds (Blumstein and Munos, 2005;Policht et al, 2009), and mammals (Frommolt et al, 1997;Darden et al, 2003;Frommolt et al, 2003). This characteristic enables the study of individual identification using only acoustic modalities.…”

Utility of vocal formant spacing for monitoring sandhill crane subspecies

“…Animal vocalizations potentially contain a variety of valuable information including the sex, age, size, and subspecific identity of the vocalizer (Fitch 1997, 1999; Riede and Fitch 1999). Vocal analysis has been suggested for population monitoring in a wide variety of taxa, including canids (Darden et al 2003, Hartwig 2005), birds (Policht et al 2009), and bats (Fukui et al 2004). Recent research on vocal identification of animals has focused on a vocal characteristic called formant spacing, or formant dispersion, because it has been shown to correlate with body size (Fitch 1997, 1999; Riede and Fitch 1999).…”