1. North Carolina Cooperative Fish and Wildlife Research Unit; Department of Applied Ecology; North Carolina State University; Raleigh North Carolina 27695 USA
2. Department of Natural Resource Ecology and Management; 339 Science II Iowa State University Ames Iowa 50011 USA
3. U. S. Geological Survey; North Carolina Cooperative Fish and Wildlife Research Unit; Department of Applied Ecology; North Carolina State University; Raleigh North Carolina 27695 USA
4. The Institute for Bird Populations; P. O. Box 1346 Pt. Reyes Station California 94956 USA