1. School of Natural Resources; University of Nebraska-Lincoln and Nebraska Cooperative Fish and Wildlife Research Unit; 013 Hardin Hall 3310 Holdrege St Lincoln NE 68583 U.S.A.
2. School of Natural Resources; University of Nebraska-Lincoln; 402 Hardin Hall 3310 Holdrege St Lincoln NE 68583 U.S.A.
3. U.S. Geological Survey-Nebraska Cooperative Fish and Wildlife Research Unit, School of Natural Resources; University of Nebraska-Lincoln; 424 Hardin Hall 3310 Holdrege St Lincoln NE 68583 U.S.A.