A new USGS report summarizes research accomplishments and results from the first 3.5 years, 2015-2018, of a study in Oregon and Washington to determine if removing barred owls can improve population trends of Northern spotted owls.
Preliminary results indicate removals were effective in reducing the territorial barred owl population by 19–43 percent over 3 years. By 2018, site occupancy and numbers of spotted owls appeared to stabilize in areas with barred owl removal but continued to decline rapidly in control areas without removals. Numbers of spotted owls remaining in study areas have reached alarmingly low levels, however, and annual reproduction in 2018 was the lowest observed in the study areas over the past 28 years. These results suggest that stabilizing declining population trends of spotted owls may require additional removal efforts. Authors recommend continuation of removal experiments in Oregon and Washington to confirm preliminary results and more accurately determine the demographic response of spotted owls to barred owl removals.
Wiens, J.D., Dugger, K.M., Lesmeister, D.B., Dilione, K.E., Simon, D.C., 2019, Effects of Barred Owl (Strix varia) Removal on Population Demography of Northern Spotted Owls (Strix occidentalis caurina) in Washington and Oregon, 2015-2018: U.S. Geological Survey Open-File Report 2019-1074, p. 17, https://doi.org/10.3133/ofr20191074.