Population dynamics and habitat use of the pueo (Hawaiian short-eared owl; Asio flammeus)

Date
2021
Authors
Wilhite, Chad Jacob
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Price, Melissa R.
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Natural Resources and Environmental Management
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Short-eared owls (Asio flammeus) are a globally distributed species inhabiting four continents and numerous island systems spanning tropical and temperate latitudes. Across the species range, short-eared owls are expected to follow global macroecological patterns in movement strategies where island populations are more resident, and experience expanded niches. To date, most studies exploring short-eared owl movement originate from North America and Europe and further research exploring these patterns throughout the species range is needed. The need for further research is highlighted by range-wide population declines of short-eared owls over the last 40 years that have increased concern for the persistence of the species. In Hawai‘i, managers suspect population declines of the endemic short-eared owl subspecies, the pueo (Asio f. sandwichensis), which is classified by the state of Hawai‘i as endangered on the island of O‘ahu. In my study I was curious how the pueo population has changed over the last decade and how pueo are moving through time and space. To assess pueo population dynamics throughout Hawai‘i, I used community science data collected over the last ten years to estimate trends in pueo occupancy, or the probability that a given site is occupied by at least one pueo. Occupancy dynamics are reflective of underlying changes in population size and the vital rates driving occupancy dynamics such as site colonization, extinction, and persistence provide insight temporal dynamics of the species distribution. To explore pueo spatial ecology further, I captured and banded five adult pueo, and attached VHF transmitters to four of the five, to track individual movements on the island of O‘ahu. I found some no evidence of small regional decline in pueo occupancy probability over the last decade. Statewide pueo occupancy probability (ψ̂) averaged 0.19 ± 0.01 SE with an estimated rate of change (λ̂) during 2011-2020 of 0.98 ± 0.01 SE, showing a slight annual decrease in occupancy. In contrast to studies of nominate short-eared owls in western North America, site turnover (τ̂), or the probability that a site occupied in one year was unoccupied in the previous year, was consistently low among years at 0.06 ± 0.01 SE providing evidence that the pueo are less nomadic. Following the movements of individual pueo tagged with VHF transmitters, I observed consistently use of both grassland and wooded habitats. The VHF tagged pueo roosted mainly on elevated perches in wooded habitats, as opposed to the short-eared owls in North America and Eurasia that are commonly described as open-habitat specialists typically roosting on the ground in open habitats. These results suggest that wooded areas should also be considered for conservation of the subspecies and that pueo in Hawai‘i may exhibit an expanded niche compared to continental owls. Further, repeat sightings of tagged individuals in subsequent years indicates that individual pueo tend to occupy the same site from year to year, providing additional support of a more resident population in Hawai‘i than short-eared owls in North America. Overall, I present evidence of slight declines in pueo occupancy, however, trends appear stable over the last decade. The models presented in this study are not predictive and factors affecting pueo occurrence and vital rates remain relatively unknown. Further research should work to identify drivers of occupancy dynamics in pueo. With the use of community science data and VHF transmitters I present findings exploring the spatial ecology of pueo, suggesting that pueo exhibit different movement ecology strategies in Hawai‘i. My small sample size precludes broad conclusions and further work should include the use of longer-lived GPS transmitters deployed at more sites throughout Hawai‘i.
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Ecology, Conservation biology, Natural resource management, community science, dynamic occupancy, habitat use, population, vhf
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78 pages
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