Ecological speciation predicts that the fitness of hybrids will be reduced if they exhibit intermediate phenotypes that fall between parental niches. Empirical support for this prediction is sparse and migratory divides may help fill this gap. Divides occur between populations with divergent migratory routes. Hybrids in divides are predicted to take intermediate routes over terrain avoided by pure forms, reducing their fitness. We test this prediction here in a well-characterized divide between Swainson's