1. Department of Environmental Science, Policy and Management, University of California at Berkeley, 151 Hilgard Hall, Berkeley, California 94720, USA
2. San Francisco Bay Bird Observatory, P.O. Box 247, 1290 Hope Street, Alviso, California 95002, USA
3. Centre for Applied Conservation Biology, Department of Forest Sciences, 3041–2424 Main Mall, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada