Climate and Land‐Use Change Leading to Niche Expansion and Shifts in Birds

ABSTRACT Aim The realised niches of species change following environmental and distributional shifts. Still, the magnitude of niche change and its consequences are determined by how different species cope with environmental changes, which ultimately depends on their ecology and traits. We assessed how environmental and distributional shifts have led to changes in the realised breeding niches of 121 species of North American birds over the last four decades and how the magnitude of niche change was associated with species traits. Location North America. Taxon Birds. Methods We calculated geographic and niche overlap, breadth and shift, and estimated the temporal trends of the different niche metrics from 1980 to 2018 for each species. The slopes of these temporal trends were then modelled as a function of species traits using Bayesian models that accounted for phylogenetic relatedness and the uncertainty of the temporal slopes. Results We found that the niche of 57% of the bird species diverged through time as they experienced widespread environmental change, including changes in both niche breadth and position. Most niches expanded due to increasing environmental variability within their ranges, but habitat specialists showed a tendency for niche contraction. Niche shifts were larger in species that live in habitats with denser vegetation cover. However, species showing larger average geographical shifts were able to track their reference niche more effectively. Main Conclusions Bird species were in general increasingly exposed to higher environmental variation that led to changes in their realised niches over a relatively short time span (four decades), while the niches of many others remained stable. The differences in the magnitude of niche change were to some extent related to species traits, providing clues about how different species respond to widespread environmental change in both geographical and niche space.