1. Wadsworth Center, New York State Department of Health and School of Public Health, State University of New York at Albany, Albany, New York 12201-0509, U.S. Geological Survey, Patuxent Wildlife Research Center, 12011 Beech Forest Road, Laurel, Maryland 20708-4041, and U.S. Fish and Wildlife Service, Chesapeake Bay Field Office, 177 Admiral Cochrane Drive, Annapolis, Maryland 21401