DONALD H. WHITE,^* CHRISTINE A. MITCHELL,^* ELIZABETH J. KOLBE,^** JAMES M. WILLIAMS<sup>***


*</sup>U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center, Gulf Coast Field Station, P.O. Box 2506, Victoria, Texas 77902, USA.
^**U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center, Laurel, Maryland 20708, USA.
^***U.S. Fish and Wildlife Service, Hagerman National Wildlife Refuge, Route 3, Box 123, Sherman, Texas 75090, USA.