Intraspecific Variation in Home Range Size, Overlap, and Movement Behaviors of ‘Io - the Hawaiian Hawk (Buteo solitarius)

Abstract

‘Io (Buteo solitarius) is the only endemic hawk species across the Hawaiian archipelago and their range is restricted to Hawai‘i Island. Their federal delisting in 2020, alongside their cultural and ecological significance, emphasizes the importance of sustained long-term population monitoring efforts. However, existing home range estimates for the species are outdated, and research on their spatial behaviors remains deficient. This study aimed to update ‘io home range estimates while providing insights into their movement strategies and space-use sharing patterns. From June 2022 to October 2023, solar GPS-GSM transmitters tracked 43 ‘io on the east side of Hawai‘i Island. Using continuous-time stochastic process (CTSP) models and an autocorrelated kernel density estimator (ADKE), the estimated median home range size for the population was 616 hectares, which is larger than previous estimates obtained using traditional tracking and analysis methods. Although no significant difference in home range size existed across sex and age groups, it varied based on movement strategy. Birds whose movement patterns remained within a distinct range had smaller home ranges overall than those engaging in an occasional foray or commuting between multiple ranges. Additionally, all individuals within the population shared on average 10% of space, with up to 97% observed between presumed breeding pairs. A high likelihood of pairwise encounters was predicted to occur not only along home range boundaries but also within core areas, indicating a high potential for intraspecies interactions. This study provides new insights into ‘io spatial behaviors and highlights the importance of advanced technology and analytical tools to aid species conservation.