Spatial and temporal scale-dependence of the strength of migratory connectivity in a North American passerine 

Background: Migratory connectivity describes the extent to which portions of a migratory population that are spatially associated during one stage of the annual cycle remain associated during other stages of the annual cycle. The strength of migratory connectivity may vary spatially across a species’ range and temporally as individuals move through stages of their annual cycle. Few studies have quantified this spatial and temporal variation in the strength of migratory connectivity within a single species. Methods We investigated spatial and temporal variation in the strength of migratory connectivity in Painted Buntings ( Passerina ciris ), a small migratory bird that, uniquely among North American songbirds, breeds in disjunct eastern and western populations. Using tracking data from 113 individuals sampled at eleven breeding sites across the species’ breeding distribution, we quantified the strength of connectivity at multiple spatial and temporal scales. Results We found strong breeding-to-winter connectivity at the range-wide scale, with interior and eastern Painted Buntings remaining separate throughout the annual cycle, but weak connectivity within populations, with individuals from different regions of both populations mixing extensively on the wintering ground. Despite weak breeding-to-winter connectivity within populations, the interior population displayed strong breeding-to-molting connectivity, with birds from different breeding sites showing distinct migratory strategies during the molting period. Conclusion These results demonstrate the extent to which the strength of migratory connectivity can vary across both space and time within a single species and underscore the importance of careful sampling design when quantifying this metric. Because inferences about the strength of connectivity can be sensitive to when and where sampling occurs, there is an urgent need for continued focus on study design regarding migratory connectivity.