Specimens were kindly provided by the Carnegie Field Museum and the Chicago Field Museum. Egg measurements from the Western Foundation of Vertebrate Zoology were provided by Clark Sumida and Lloyd Kiff. Sam Droege provided Breeding Bird Survey data. Information on behavior, distribution, and vocalizations was kindly provided by Range Bayer, Jerram Brown, R. Wayne Campbell, Sylvia Hope, Pat Kennedy, John Marzluff, Don Roberson, and Andrew Stewart. Research was supported by a U.S. Fish and Wildlife Service grant to EG; VRM was supported by a Queen's University Graduate Fellowship, Sigma Xi Grant-in-Aid of Research, Five Valleys Audubon Society, and Natural Sciences and Engineering Research Council operating grant to Laurene Ratcliffe. We thank Louis Bevier, Jerram Brown, Mercedes Davison, Donald Kroodsma, Alan Poole, Keith Russell, and Stephen Vander Wall for many helpful comments on this manuscript. Kate Davis kindly drew the jays for Figure 2.