The Service is confident that once mice are removed, most if not all burrowing owls landing on the South Farallones in the fall will continue on their migratory path and find more suitable wintering areas on the mainland, having found insufficient food resources on the islands.

Predatory bird populations on the South Farallon Islands have been monitored by biologists from Point Blue Conservation Science since 1968. This long-term data shows that most birds of prey that do not eat mice, such as Sharp-shinned Hawks and Cooper’s Hawks, do not over-winter on the Refuge even though they are occasionally present briefly during the fall migration period. In contrast, the mouse-eating Burrowing Owls have a much higher tendency to spend the winter on the South Farallones.