Estimation of population size and sex ratio of Ryukyu Scops Owl Otus elegans on Hateruma Island

Abstract

Fundamental demographic data of insular populations of Otus owls are not available for most species. This study investigated the population size and the sex ratio of the Ryukyu Scops Owls Otus elegans on Hateruma Island. Capture-recapture data was obtained by intensive marking and route census surveys from July to September in 2021. Analysing the data using a site-occupancy model combined with a data-augmentation technique, the population size was estimated as 155.470 individuals (97.575 males and 57.895 females), with a significant male-biased sex ratio (0.631).