Barred Owls Intensify Northern Spotted Owl Decline

[Cara J]

Populations of federally threatened northern spotted owls (Strix occidentalis caurina), a subspecies native to the western United States, continue to dwindle. The reason? Competition with the barred owl (Strix varia) — a highly adaptable species that has expanded its range westward from the eastern United States and Canada, according to a study led by Katie Dugger, assistant unit leader at the USGS Oregon Cooperative Fish and Wildlife Research Unit and an associate professor at Oregon State University. The study was recently published in The Condor: Ornithological Applications. “In our most recent analysis, we got better data on barred owls in particular,” said Eric Forsman, a coauthor in the study who is a retired U.S. Forest Service Research biologist and member of The Wildlife Society. Dugger, Forsman, and their colleagues examined the most recent spotted owl population data from 11 long-term demography study areas in California, Oregon and Washington State. They used mark-recapture models and occupancy models to examine relationships between trends in the owl population and variables such as the amount of old forest cover, climate conditions and the presence of competitors such as barred owls. “Barred owls now outnumber spotted owls on some of our study areas and in [...]

 

Read more: http://wildlife.org/barred-owls-intensify-northern-spotted-owl-decline/