1. Illinois Natural History Survey, Prairie Research Institute, University of Illinois Urbana–Champaign, Champaign, IL 61820, USA.
2. Frank C. Bellrose Waterfowl Research Center, Forbes Biological Station, Illinois Natural History Survey, Prairie Research Institute, University of Illinois Urbana–Champaign, Havana, IL 62644, USA.
3. U.S. Fish and Wildlife Service, Hatchie National Wildlife Refuge, 6772 Highway 76 South, Stanton, TN 38069, USA.