Abstract

Each year, seasonal bird migration leads to an immense redistribution of species occurrence and abundances, with pervasive, though unclear, consequences for patterns of multi-faceted avian diversity. Here, we uncover stark disparities in spatiotemporal variation between avian taxonomic and functional diversity across the continental US. In the eastern US, the temporal patterns of taxonomic and functional diversity are diametrically opposed, with functional richness highest in winter despite seasonal loss of species, and the remaining most abundant species amassed in a few regions of the functional space that likely reflect the resources available in winter. In contrast, in the western US, both species and functional richness are high during the breeding season, and species' abundances are regularly distributed and widely spread across the functional space. We anticipate that the uncovered complexity of spatiotemporal associations among avian diversity measures will be the catalyst for adopting an explicitly temporal framework for multi-faceted biodiversity analysis.