Barred owls ousting spotted owls in the Northwest

An increase in the barred owl population is contributing to the decline of threatened Northern spotted owls, according to models developed by U.S. Geological Survey and U.S. Forest Service scientists. A report on the models was released Monday by the U.S. Geological Survey in Flagstaff, Ariz. The larger barred owl is considered to be a more aggressive competitor, with higher reproductive capacity as well as a more diverse diet and use of habitat. In the face of increasing barred owl populations and declining habitat, the medium size Northern spotted owl, which lives in old growth forests of northern California and the Pacific Northwest of the United States, is declining. Using 22 years of detection data from a 1,000 square kilometer site in Oregon, researchers found that both species are more likely to abandon an area when the other species is present. “While both species feel the effects of competition, spotted owls are far more sensitive,” said Charles Yackulic, a USGS research statistician and lead author of the study. “As a result, spotted owls at this site, and in many other areas, are declining while barred owl numbers steadily increase.“ The authors simulated future population dynamics and found that barred owls are likely to drive down spotted owls to low numbers over the next few decades. “Scientists in other parts of the Pacific northwest have suggested that differences in the habitat preferences of the barred owl and spotted owl might allow them to coexist. While the two species showed different habitat preferences in this study site, there is still substantial overlap in habitat use,” said Yackulic. “As a result, in recent years, barred owls have frequently excluded spotted owls from habitat that they would otherwise prefer.“...more