But because it is so rare to find a spotted owl dead in the forest, the scientists will look at an invasive cousin owl that's pushing spotted owls out of their territory.
Mourad Gabriel, a doctoral candidate at the University of California, Davis, says that tests are being done on 84 barred owls killed as part of research on whether removing them allows spotted owls to reclaim lost territories.
He said Tuesday that among the first owls tested, about half carried the poison.
The research is funded primarily by the U.S. Fish and Wildlife Service.