Publisher's Synopsis
Differentiation and speciation without extended isolation appear to be common among migratory animals. Historical oversight of this is probably due to temporal distortion in distribution maps and a tendency to consider that lineages had different historical traits, such as being sedentary or much less mobile. Mobility among cyclic migrants makes population isolation difficult, and diminished levels of intraspecific differentiation occur in avian migrants (I term this "Montgomery's rule"). Nevertheless, many lineages have differentiated despite increased mobility and a high propensity for gene flow, conditions that speciation theory has not addressed adequately. Populations of seasonal migrants usually occur in allopatry and sympatry during a migratory cycle, and this distributional pattern (heteropatry) is the focus of a model empirically developed to explain differentiation in migratory lineages. Divergence arises through disruptive se
