Vocalisations of the Christmas Island Hawk-Owl Ninox natalis: Individual Variation in Advertisement Calls

Abstract

Six different calls of the Christmas Island Hawk-Owl Ninox natalis were recorded during a two-year study of its biology. These vocalisations showed many structural and functional similarities with those described for the Southern Boobook N. novaeseelandiae. Of 195 advertisement calls by 11 owls, 91.3% were correctly attributed to an individual using a multiple discriminant analysis model comprising five measurements of call frequency and duration. We provide some evidence for the calls of individuals being constant over time. Individual variation in advertising calls may have some use in estimating owl densities, especially in areas where the terrain makes traditional techniques such as radio-tracking impractical.