The study, released Jan. 11 in the journal Avian Conservation and Ecology, showed that seven of the 10 northern spotted owls collected tested positive for rat poison, while 40 percent of 84 barred owls collected also tested positive for the poison.
The study is the first published account of anticoagulant rodenticide in northern spotted owls, which are listed as a threatened species under federal and state Endangered Species acts.
It supports previous accounts that rat poison is contaminating the food web in this region, as the primary food source for owls — rodents — is being contaminated.
These sites often overlap with designated critical habitat for northern spotted owls, and the owls feed at their edges.
Barred owls are a physically larger group of owls currently competing for resources and space in critical habitat designated for northern spotted owls.
Forty percent, or 34 of 84, of the barred owl tissue samples collected for this study tested positive for anticoagulant rodenticide.
Environmental contamination, when coupled with ongoing competition from barred owls, poses an additional stressor on northern spotted owls, the study said. »