Short-Eared Owl Land-Use Associations during the Breeding Season in the Western United States

Abstract

The Short-eared Owl (Asio flammeus) is a species of conservation concern in the western USA, with evidence for declining population sizes. Monitoring of Short-eared Owls is complicated because of their low site fidelity and nomadic movements. We recruited community-science participants to implement a multi-year survey of Short-eared Owls across eight states in the western USA, resulting in a program of sufficient temporal and spatial dimensions to overcome many of the challenges in monitoring this species. We implemented both multi-scale occupancy and colonization/extinction modeling to provide insights into land-cover use, and to identify which cover types supported higher occurrence. Short-eared Owls were associated with native and anthropogenic land-cover types, but site occupancy varied among these categories and at different scales. Native grasslands, marsh/riparian, hay/fallow agriculture, and cultivated croplands were occupied most consistently across years. Occupancy rates differed at different scales (e.g., marsh/riparian was the only land-cover type positively associated with occupancy at both transect and point scales). Contrary to expectations, native shrubland was negatively associated with occupancy at the point scale, and exhibited low colonization and high extinction rates. Our results suggest that conserving native landscapes in general, and grasslands, marsh, and riparian areas specifically, would benefit Short-eared Owls. Furthermore, Short-eared Owl occupancy was positively associated with hay/fallow land-cover types, suggesting that some nonnative land-cover types can function as Short-eared Owl habitat. Lastly, our results highlight how developing a broad-scale community science survey can inform conservation for a species not well monitored by existing survey programs.

Temporal and spatial population dynamics of the nomadic short‐eared owl across the western United States

“…Only Utah and Washington were reasonably stable, with 2019 occupancy estimates similar to other years. All surveys in Utah with owl detections had some marshland present, and most had hay or fallow agriculture present, both important land covers for this species in our region as identified in Miller et al (2022). Most of the owl detections in Utah occurred in lowlands near the Great Salt Lake where rivers and streams form marshes and deltas before flowing into the lake.…”

“…Most of the owl detections in Utah occurred in lowlands near the Great Salt Lake where rivers and streams form marshes and deltas before flowing into the lake. These landscapes have some of the highest site fidelity, which we defined as site occupancy by the species and not necessarily by the same individuals, for short‐eared owls in the western United States (Miller et al 2022). We expect that in habitats where small‐mammal populations are more diverse, we would see a dampened prey cycle, assuming that different species cycle at different times, and this could result in higher site fidelity by short‐eared owls (Newton 2006), which might be an explanation for why short‐eared owls in these habitats have higher site fidelity.…”

“…We provided participants with 2 3-week survey windows, depending upon latitude and elevation, during our March through May survey season in which to perform each survey. We selected the survey windows for each grid cell to best account for the expected period of short-eared owl courtship flight behavior, a time of maximum detectability (Larson and Holt 2016;Miller et al 2016Miller et al , 2022. Although participants could choose any day within the survey windows to perform each survey, we requested that the 2 visits be ≥1 week apart if possible.…”

“…We conducted our study in 8 states in the western United States: California (423,967 km 2 ), Idaho (216,443 km 2 ), Montana (380,831 km 2 ), Nevada (286,380 km 2 ), Oregon (254,799 km 2 ), Utah (219,882 km 2 ), Washington (184,661 km 2 ), and Wyoming (253,335 km 2 ). Participants conducted surveys in all states between 2018 and 2020 for this study, with Idaho, Nevada, Utah, and Wyoming involved in pilot or early implementation efforts in 2016 and 2017 (Miller et al 2016(Miller et al , 2022; Figure 1). The study area included coastal zones at or near mean sea level, and mountain ranges up to 4,421 m above mean sea level.…”

“…In North America, the short‐eared owl ( Asio flammeus ) is associated with grasslands and related cover types that have experienced human modification (Holt et al 1999, Wiggins et al 2020, Miller et al 2022). In addition, the short‐eared owl has experienced a population decline possibly exceeding 60% since the 1970s (Booms et al 2014, Stanton et al 2018, Rosenberg et al 2019).…”