The Short-eared Owl (Asio flammeus) is an open-country species that breeds in the northern United States and Canada, and has likely experienced a long-term, range-wide population decline. However, the cause and magnitude of the decline are not well understood. The Western Asio flammeus Landscape Study (WAfLS) program is a multi-year, eight-state survey program for Short-eared Owls, implemented largely by community-science volunteers. We address four objectives within the WAfLS program: 1) better define and protect important habitats; 2) improve population monitoring; 3) better understand regional owl movements; and 4) develop management plans and tools. Population monitoring of Short-eared Owls is complicated by the fact that the species is an irruptive breeder with low site fidelity, resulting in large shifts in local breeding densities, often tied to fluctuations in prey density. We recruited 622 participants in 2018, and 605 participants in 2019, to survey at study sites in California, Idaho, Montana, Nevada, Oregon, Utah, Washington, and Wyoming. We surveyed 368 and 334 transects in each year respectively, and detected Short-eared Owls on 57 transects in each year. We performed multi-scale occupancy and maximum entropy modeling to identify population status, habitat and climate associations.
Results/Conclusions
As compared to 2018, our 2019 estimated occupancy rates suggest an annual increase in breeding density in the northern and eastern states, most strongly in Montana, followed by Washington, Wyoming, and Utah. Idaho, Nevada, Oregon, and California had lower breeding densities than in 2018. Short-eared Owl occupancy is highest at points with complex grassland, fallow agriculture fields, and lower levels of grazing. In contrast to 2018, shrubland landscapes were not favored in 2019, influenced by the shift in breeding density toward eastern Montana. Transect-level occupancy was most strongly associated with grasslands, hay, and fallow fields, with orchards and vine crops specifically avoided. Short-eared Owls have a climate association that puts them at great risk, given their apparent preference of landscapes with higher relative precipitation and moderate seasonality. As our summers continue to become drier, we expect a further decrease in the population of this species, possibly through the climate’s effect on prey abundance. Our results also demonstrate the feasibility, efficiency, and effectiveness of utilizing community scientists to achieve a robust sampling methodology across the broad geography of the western United States.