Assessing ‘Ōpe‘ape‘a Habitat Use and Occupancy in the Helemano Wilderness Area, Central O‘ahu

Abstract

‘Ōpe‘ape‘a, the Hawaiian hoary bat (Lasiurus semotus), is the only extant, native, terrestrial land mammal in Hawai‘i. It has been listed as endangered under the Federal Endangered Species Act and Hawai‘i Endangered Species Laws since 1970. Despite this level of protection, there are large gaps in scientific understanding of this species’ general ecology. This is especially true on the Island of O‘ahu, where the bat’s population is thought to be the smallest of the main Hawaiian Islands. To better inform land management decisions, I examined how ‘ōpe‘ape‘a utilizes habitat in a diverse, 650 ha portion of Helemano Wilderness Area (HWA) that was purchased to protect and preserve vital bat habitat in central O‘ahu. I deployed ultrasonic acoustic detectors for one to two-week sampling periods at 80 sites across four habitat types (grazed grassland, ungrazed grassland, grazed evergreen forest, and ungrazed evergreen forest) from December 2019 to March 2020. Results from the 672 detector nights and 8,064 detector hours indicate that while bat detections were low (39 detections), bats are present in all habitat types, with the highest detection rate in grazed grassland (15 detections). The overall naïve occupancy rate across habitats was 35%. The best single species, single season occupancy model that considered habitat type, total nightly rainfall (mm) and month showed no statistically significant difference for occupancy between the four different habitats (P Value >0.05). However, detection probability was statistically different by month with the fewest detections occurring in December (P<0.05). In addition, while not statistically significant (P>0.05), total nightly rainfall (mm) had a negative association with detection rate as an increase in rainfall was correlated with a decrease in bat detections. Results from this study will provide a habitat use baseline for HWA, which will inform land use management decisions by the State of Hawaiʻi. In addition, this study increases understanding of the basic ecology of an understudied endangered species, which will be useful for land managers statewide.