USDA National Wildlife Research Center Symposia


Date of this Version



Published in: Witmer, G. W., W. C. Pitt, and K. A. Fagerstone, editors. 2007. Managing vertebrate invasive species: proceedings of an international symposium. USDA/APHIS Wildlife Services, National Wildlife Research Center, Fort Collins, Colorado, USA. Also available online at


Invasive, but native to North America, barred owls (Strix varia) are negatively affecting site occupancy, reproduction, and survival of federally threatened northern spotted owls (Strix occidentalis caurina), thereby confounding the land-based conservation strategy for northern spotted owls. Barred owls are moving southward into the range of non-federally listed California spotted owls (S. o. occidentalis), but are not, at this time or in the foreseeable future, a threat to the California spotted owl population. We recommend consideration of barred owl control in the northern Sierra Nevada Mountains, while barred owl numbers are low enough to efficiently eliminate the possibility that they negatively affect California spotted owls outside of the foreseeable future.