1. Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, One Shields Avenue, Davis, California 95616, USA
2. California Department of Fish and Wildlife, Bay Delta Region (3), 2109 Arch Airport Road, Stockton, California 95206, USA
3. Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, 944 Garrod Drive, Davis, California 95616, USA
4. Department of Biological Sciences, California State University, Sacramento, 6000 J Street, Sacramento, California 95819, USA