The strength of migratory connectivity in Painted Buntings is spatial scale dependent and shaped by molting behavior

Abstract

As migratory species move through the stages of their annual cycle, individuals often display variation in the degree to which they remain in proximity to one another, a phenomenon called migratory connectivity. We show scale dependence in the strength of migratory connectivity in Painted Buntings (Passerina ciris), a North American passerine with disjunct eastern and interior breeding populations. Based on light-level geolocator data from 112 individuals at 11 breeding sites, migratory connectivity between breeding and wintering grounds was strong at the range-wide scale, with interior and eastern Painted Buntings remaining separated throughout the annual cycle. Conversely, migratory connectivity within the eastern and interior populations was weak, with individuals from different breeding areas mixing extensively on winter quarters. We found weak migratory connectivity within populations as birds moved from the breeding grounds to the wintering grounds (breeding-to-winter), with individuals from different regions of each population mixing extensively on the wintering grounds. The interior population, however, displayed strong migratory connectivity as birds moved from the breeding grounds to the intermediate molting grounds (breeding-to-molting), with birds from different breeding sites showing contrasting migratory strategies during the molting period. Our results suggest that spatial scale dependence of migratory connectivity is likely to be a pervasive phenomenon, given that migratory routes and the likelihood of molt migration often differ among populations. When possible, researchers should be deliberate about the spatial design of tracking studies to reduce potential biases that can result from spatial scale-dependent migratory connectivity. © 2023 by the author(s). Published here under license by the Resilience Alliance.