Short-eared Owl 2017 Annual Report

In 2017 a large group of volunteers sampled a broad geography within the Intermountain West. The abundance estimates and habitat associations results from this effort provides critical insight to land managers across the Intermountain West to influence species-specific general conservation actions. CLICK HERE TO VIEW PDF. 

2017 Western Asio flammeus Landscape Study (WAFLS) Annual Report

Robert A. Millera (a,1), Neil Paprocki (b), Bryan Bedrosian (c), Cris Tomlinson (d), Jay D. Carlisle (a), and Colleen Moulton (e)

a. Intermountain Bird Observatory, Boise, Idaho, USA
b. HawkWatch International, Salt Lake City, Utah, USA;
c. Teton Raptor Center, Wilson, Wyoming, USA;
d. Nevada Department of Wildlife, Las Vegas, Nevada, USA;
e. Idaho Department of Fish and Game, Boise, Idaho, USA
1. Correspending author: RobertMiller7@boisestate.edu; 208-860-4944

Project WAFLS 2017 Annual Report 2

ABSTRACT. The Short-eared Owl 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 is not well understood. Following Booms et al. (2014), who proposed six conservation actions for this species, we set forth to address four of these objectives within this program: 1) better define and protect important habitats; 2) improve population monitoring; 3) better understand 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 swings in local breeding densities, often tied to fluctuations in prey density. It is therefore, critical that any monitoring effort be implemented on a broad enough scale to catch regional shifts in distribution that are expected to occur annually. We recruited 330 participants, many of which were citizen-science volunteers, to survey over 41 million ha within the Intermountain West states of Idaho, Nevada, Utah, and Wyoming during the 2017 breeding season. We surveyed 181 transects, 163 of which were surveyed twice, and detected Short-eared Owls on 18 transects. We performed multi-scale occupancy modeling, multi-scale abundance modeling, and maximum entropy modeling to identify population status, habitat and climate associations. While we had an insufficient number of detections this year for specific abundance estimation, our occupancy rates suggest a significant decrease in population size this breeding season in Idaho and Utah, possibly exceeding 60%, as compared to recent years. As expected, our occupancy modeling found that the probability of detecting Short-eared Owls was impacted by the time of the survey and local wind conditions. We most often found Short-eared Owls in areas with moderate levels of grazing, exceeding areas with no grazing and those where the whole landscape was open to grazing, an association we have not found in past years. Consistent with recent years, Short-eared Owls were more likely in areas of shrubland, cropland, and marshland, and less likely in areas of grassland. On the surface, our results may seem contradictory to the presumed land use by a “grassland” species; however, many of the grasslands of the Intermountain West, consisting largely of invasive cheatgrass, lack the complex structure shown to be preferred by these owls. Our results suggest that Short-eared Owls have a climate association that puts them at great future risk, primarily their apparent preference of landscapes with high precipitation and moderate seasonality. As our summers continue to dry, as is expected under most climate scenarios, we would expect a further decrease in the population of this species, possibly through the climate’s effect on prey abundance. As a result of the consistent results across the broad scale of the program, we have established with high confidence that the breeding density of Short-eared Owls in 2017 was much lower than recent years and that the birds did not simply shift distribution within the region. Lastly, our results demonstrate the feasibility, efficiency, and effectiveness of utilizing public participation in scientific research (i.e., citizen scientists) to achieve a robust sampling methodology across the broad geography of the Intermountain West. We look forward to the continued expansion of this program in future years.