1. National Council for Air and Stream Improvement, Forestry and Range Sciences Lab, 1401 Gekeler Lane, La Grande, Oregon 97850, USA
2. Ecology Department, Montana State University, 310 Lewis Hall, Bozeman, Montana 59717, USA
3. National Council for Air and Stream Improvement, P.O. Box 68, Stevensville, Montana 59870, USA
4. Conservation and Research Center, National Zoological Park, Smithsonian Institution, Front Royal, Virginia 22630, USA