Factors influencing the distribution of the Hawaiian short-eared owl (pueo) on the island of Maui, Hawai‘i

Abstract

Multiple factors influence the selection of foraging habitat in raptors. To conserve energy, many raptor species tend to hunt in areas with reduced cover for ease of prey detection and capture, but prey type and availability varies across the landscape and also influences distribution. The pueo, or Hawaiian short-eared owl (Asio flammeus sandwichensis), occurs across the Hawaiian Islands in diverse habitats, including forests, grasslands, wetlands, and shrublands, and consumes a variety of prey items including rodents, birds, and invertebrates. In my thesis research I evaluated which factors influence pueo occupancy on the island of Maui. I expected that the pueo would hunt in areas that were the most accessible (short vegetation and low ground cover) compared to areas with dense vegetation, and that the biomass of prey items most commonly found in pellets (mice and zebra doves) would play a greater role in predicting pueo presence than all potential prey items combined. Using a random stratified design to sample across environmental gradients, I conducted point count surveys for birds and bats, mark-recapture surveys for rodents, and sweep net surveys for insects (Order Orthoptera). Pueo were detected across a range of vegetation characteristics but were most often seen in mid to high elevation, using both open and forested areas. The detectability of pueo was influenced by vegetation height. The top single-season occupancy models indicated that bird biomass, relative total prey biomass, and ground cover were slightly negatively correlated with the estimated likelihood of pueo occupancy, while elevation, relative insect (Order Orthoptera) biomass, and vegetation height were slightly positively correlated with the estimated likelihood of pueo occupancy. Given the weak correlations observed in this study, factors other than vegetation complexity and prey biomass are also likely influencing occupancy. However, the number of detections of pueo in the study were low (n=11) and may have decreased my ability to detect stronger correlations. Future studies should investigate seasonal differences, home range size, and available nesting habitat, in relation to occupancy. As individual pueo may exhibit preferences for particular prey types and vegetation characteristics, further research tracking individual pueo for specific behaviors is needed to elucidate variation within and among island populations.