An integrative framework for understanding the origin and evolution of avian migration

John H. Rappole, Smithsonian Conservation and Research Center, 1500 Remount Road, Front Royal, VA 22630, USA. E-mail: Barbara Helm, Max-Planck Research Centre for Ornithology, D-82346 Andechs, Germany. E-mail: Mario A. Ramos, Global Environment Facility, World Bank, 1818 H St., NW, Washington, D. C., USA, E-mail: