lOak Creek Lab 0/ Biology, Department 0/ Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331, USA; 'Department 0/ Migration & immunoecology, Max Planck institut/iir Ornithologie, D-78315 RadolJzell am Bodensee, Germany; 3Department 0/ Animal Science, University o/California, Davis, California 95616, USA; 'Department o/Natural Resources & Environmental Science, University 0/ Illinois, Urbana, Illinois 61801, USA; 'Program in Ecology, Evolution & Conservation Biology, University o/Illinois, Urbana, Illinois 61801, USA; and 6Department a/Biology, University 0/ Missouri, St. Louis, Missouri 63121, USA