Investigating spatiotemporal distribution and habitat use of poorly understood procellariiform seabirds on a remote island in American Samoa

Abstract

Seabirds are important components of marine and terrestrial ecosystems across the globe, ranging across all oceans, adapted to all environments, and using both marine and terrestrial ecosystems. The island of Ta‘ū in American Samoa is not well studied, yet is home to a potentially significantly important breeding population of a suite of Procellariiform seabirds, the Tahiti Petrel (Pseudobulweria rostrata), and Tropical Shearwater (Puffinus bailloni). Because many of these birds are difficult to locate and study due to their nocturnal nature, and nesting locations in burrows at the top of a mountainous remote island, Automated Recording Units (ARU) provide a useful tool to learn about these species. I investigated the differences in detection probability for ARUs under different habitat and environmental conditions. Further, I used automated recording units to determine the spatiotemporal activity patterns of a suite of seabird species over the summit area of Ta‘ū. Finally, I used a Species Distribution Modeling approach to determine the habitat, physical, and environmental characteristics that affect Tahiti petrel nesting presence and the distribution of suitable habitat across the summit region of Ta‘ū. Detection ranges of ARUs varied from < 10 m in high wind conditions, up to 90 m in low wind conditions. On Ta‘ū, Tahiti petrel was the most widespread species and showed spatially and temporally different levels of acoustic activity from Tropical shearwater. Activity for Tahiti petrels was highest in April – May while Tropical shearwaters were more active in December. Tahiti petrel nesting location on Ta‘ū were best predicted by closed canopy cover and higher altitude. Of a total of 774.1 ha of montane habitat on Ta‘ū, 63.8% was covered by canopy tree species and a total of 254.1 ha was classified as most suitable for petrel nesting. These findings present evidence of the usefulness of ARUs, particularly in challenging environments. Further, these findings advance our knowledge of the ecology, behavior, and life history of datadeficient species in American Samoa and has implications for the management of these species and the montane habitat on Ta‘ū