Interpreting Feral Goat (Capra hircus) Movement to Guide Management in a Mesic Watershed on Oʻahu, Hawaiʻi

Abstract

Endemic Hawaiian ecosystems evolved without ungulate herbivores. Feral goats, a common nonnative ungulate on Pacific Islands, browse and trample vegetation which can denude watersheds and expose them to soil erosion. Since 1993, the Hawaiʻi Division of Forestry and Wildlife has actively suppressed feral goat populations to protect critical watersheds in a 1600-ha management area on Mount Kaʻala in the leeward Waiʻanae mountain range of Oʻahu. Despite these ongoing efforts, total eradication has not been achieved to date. This study examined the movement patterns of one male and one female feral goat in this management area over one year in 2015-16 with GPS collars. The primary objective was to determine if feral goat movements are related to seasonality, moon phase and precipitation to inform future management efforts. The male goat exhibited a large range, extending out 2.5 km from its starting point and over an 800m elevation range within the year, traveling to lower elevations during the summer months. The female goat, in turn, had a much smaller range and stayed relatively close to its initial starting point. The male goat exhibited greater movement at night than during the day, and this was particularly evident during full moon phases; animals also exhibited aversion to movement during precipitation events. Hot spot analyses showed that the female was largely confined to one location throughout the course of the study, while the male moved to multiple locations but displayed a strong affinity to the eastern portion of the management area in the Fall season. These initial findings help build knowledge on local patterns of feral goat movement within this managed area that can be used for control efforts. GPS collars provided useful high-resolution data to support further adoption of this technology to better inform management decisions. Future management strategies should incorporate longerterm movement data sets from multiple individuals to better understand habituation (e.g., return to favored locations), patterns of sexual segregation and rutting. This would allow a more demographic approach for maintaining populations below levels that are considered detrimental to this critical habitat.