In the summer of 2003, we located a territorial hybrid between the Spotted Owl (Strix occidentalis) and the Barred Owl (S. varia) in the Rubicon River watershed, Placer County, in the Sierra Nevada (latitude 38° 57′ N, longitude 120° 29′ W). The individual was located in the same general area on six occasions, and it may have displaced a pair of Spotted Owls from this area. We trapped Spotted Owls and color-banded them in this area each year from 1993 to 2002. We found the pair of Spotted Owls that occupied this area in 2002 defending a different area 4.5 km to the southwest in 2003. On four occasions, we found the hybrid owl roosting in a natural cavity in a Black Oak (Quercus kelloggii). This cavity had been used as a nest site by Spotted Owls in 3 of the past 10 years.