Three birds with one stone? Sex ratios of seized critically endangered helmeted hornbill casques reveal illegal hunting of males, females and juveniles

Abstract

Hunted wildlife can often be used to answer questions about wild individuals. Sex ratios of hunted individuals can be important for understanding changes in population demographics and viability. Here we determined the sex ratio of the illegally hunted helmeted hornbill Rhinoplax vigil, a critically endangered species from Southeast Asia, to examine their vulnerability to hunters. Using casques seized in Hong Kong SAR between 2012 and 2016, we identified the sex of seized individuals using morphological and molecular methods as well as discriminant analysis. As R. vigil females can spend up to 6 months of the year sealed into tree cavity nests, they are reliant on males for food. The unique breeding ecology of this elusive species means that males are more likely to be observed than females throughout the year. These behavioural differences mean that there are several potential outcomes which may be observed in the sex ratio of the seized casques, depending on hunting strategies. Our results suggest that sex identification is possible via visual inspection of the gular skin colour and beak‐tip markings, but when these are not available, genetic methods or morphological measurements can be used. Our findings also indicated a primarily male‐biased sex ratio across the seizures; however, females, as well as juveniles, were also present in seizures. Although removing one sex from the wild can cause shifts in demographic dynamics over time, illegal and unsustainable hunting of any measure of a critically endangered species will ultimately heighten its risk of extinction. These methods and results are useful to conservationists and researchers interested in further study of hornbill populations and their viability and are ultimately important for the conservation and management of this critically endangered species.

Causes and consequences of pair-bond disruption in socially monogamous species

“…Human activities can influence pair-bond dynamics through various means, including selectively removing partners based on sex-biased harvest rates that target specific sizes and secondary sexual traits (Milner, Nilsen, and Andreassen 2007). In monogamous species in which both sexes provide parental care, selective removal of one sex is predicted to have a stronger impact on population growth than random removals (Bessa-Gomes, Legendre, and Clobert 2004;Shyu and Caswell 2018), with evidence from empirical studies in birds (Hatten et al 2022;Jenouvrier et al 2010) and mammals (Parker, Rosell, and Mysterud 2006). Furthermore, human activities potentially affect pairbond disruption without being directly targeted, such as through sex-biased bycatch (Gianuca et al 2017).…”