The role of vocalisation for the Philippine hornbills' ecology and speciation and their implication in understanding speciation is not well understood. We described and compared recorded calls of seven hornbill taxa in captivity namely Mindanao Wrinkled hornbill (Rhabdotorrhinus leucocephalus), Rufous-headed hornbill (Rhabdotorrhinus waldeni), Luzon Rufous hornbill (Buceros hydrocorax hydrocorax), Samar Rufous hornbill (Buceros hydrocorax semigaleatus), Mindanao Rufous hornbill (Buceros hydrocorax mindanensis), Mindanao Tarictic hornbill (Penelopides affinis), Samar Tarictic hornbill (Penelopides samarensis), Visayan Tarictic hornbill (Penelopides panini) and Luzon Tarictic hornbill (Penelopides manillae), as well as comparison with the non-native Papuan hornbill (Rhyticeros plicatus). Vocalisation analysis included call duration, minimum frequency, maximum frequency, bandwidth and peak frequency. For each species in the sample, the mean and standard deviation were used to calculate the Cohen’s d statistic by using an effect size calculator. Results showed that the effect size for minimum frequency was small for P. panini vs. P. samarensis and B. hydrocorax vs. B. h. mindanensis. However, bandwidth, duration, minimum frequency, maximum frequency and peak frequency have large effect sizes for the rest of the allopatric species pairs. Hornbills' conspicuous resonating calls are sufficiently quantifiable for bioacoustic analysis and may provide new insights for their taxonomic review.
