Movement and Sexual Dimorphism of the Endangered Hawaiian Coot, (Fulica alai), on Oahu

Abstract

The endangered Hawaiian Coot, Fulica alai, is one of only six native waterbird species remaining in the Hawaiian Islands. Most of its population is concentrated in the wetlands of the islands of Kauai and Oahu. Oahu also has the most wetland loss and fragmentation. This study aimed to determine if the species exhibits sexual dimorphism, if shield size of either sex exhibits seasonal variation, and if morphometric measurements could be used to predict sex accurately, as an alternative to molecular sexing. It also sought to determine if wetland loss and fragmentation prevents movement between wetlands and how common intraisland and interisland movements are. Sixty coots were captured from five Oahu wetlands, tagged with neck collars, and standard morphometric measurements and blood samples (for molecular sexing) were taken. Resight data were collected from ten Oahu wetlands from November 2011 to December 2013. The sex ratio was heavily male biased. No morphological character tested differed significantly between the sexes when assessed independently. However, stepwise binary logistic regression indicated tarsus length, bill height, tail length, and wing length in combination differed between the sexes. Shield size of males exhibited a significant declining trend over the year, being larger in males captured during the pre-breeding and breeding season and smaller in those captured during the post-breeding season. Female shield size did not vary significantly among seasons. The accuracy of predicting sex based on regression models of morphometric measurements was insufficient to substitute for molecular sexing. Habitat fragmentation did not preclude movement, intraisland movement was common and even the widest channels between islands did not impede interisland movement. Movement was not associated with sex, wing length or wing loading. Analysis of resight histories indicated encounter probability was lower during the pre-breeding and early breeding seasons than the late and post-breeding seasons.