Pervasive poleward shifts among North American bird species

Abstract

Climate change is expected to influence species' geographic distributions in the form of poleward and upward range expansion combined with extirpations from the equatorial and downslope sides of the distribution, but such shifts observed to date have been relatively subtle. Such shifts would be driven by changing patterns of fitness under changing conditions, producing population responses that would then be followed by range expansions and retractions. Here, we demonstrate pervasive population trends across the North American avifauna, reflected in the mean latitudinal position across all individuals of each species, conservatively estimated as affecting nearly half of the species in the avifauna. This result appears to constitute an intermediate step that would likely translate into concrete range shifts in numerous species over coming decades. We take this bellwether as a signal that climate change processes are affecting a significant proportion of North American bird species, and that biodiversity conservation and protected areas planning and management strategies in the region will need reexamination and re-planning in light of likely population trends and range shifts.