Broad-scale Seasonal Climate Tracking is a Consequence, Not a Driver, of Avian Migratory Connectivity.

Tracking climatic conditions throughout the year is often assumed to be an adaptive behaviour underlying seasonal migration patterns in animal populations. We investigate this hypothesis using genetic markers data to map migratory connectivity for 27 genetically distinct bird populations from 7 species. We found that the variation in seasonal climate tracking across our suite of populations at a continental scale is more likely a consequence, rather than a direct driver, of migratory connectivity, which is primarily shaped by energy efficiency-i.e., optimizing the balance between accessing available resources and movement costs. However, our results also suggest that regional-scale seasonal precipitation tracking affects population migration destinations, thus revealing a potential scale dependency of ecological processes driving migration. Our results have implications for the conservation of these migratory species under climate change, as populations tracking climate seasonally are potentially at higher risk if they adapt to a narrow range of climatic conditions. Contrary to a commonly held assumption, this study shows that the variation in seasonal climate tracking across a suite of genetically distinct bird populations is more likely a consequence, rather than a direct driver, of migratory connectivity. We found that broad-scale intraspecific migration patterns are primarily shaped by optimizing the balance between accessing available resources and movement costs, but that regional-scale seasonal precipitation tracking also affects population migration destinations, thus revealing a potential scale dependency of ecological processes driving migration. Our results have implications for the conservation of migratory species under climate change, as populations that track climate seasonally are potentially at higher risk if they adapt to a narrow range of climatic conditions.image