Biomass and abundance trends diverge as the North American avifauna undergoes widespread demographic declines

Biomass is a fundamental metric in ecology and conservation, widely used to inform questions related to community structure, energetics and function. Despite the ubiquity of biomass in broader ecological research, avian ecology and conservation has been based primarily on measures of abundance. Here, we re‐examine a recent study in avian conservation that found a net loss of three billion North American birds from 1970–2017. We augment this analysis by calculating change in overall avian biomass during the same period. Counterintuitively, we find that avian biomass across the continent has increased by 11% despite a 29% decline in abundance. Substantial restructuring in the biomass of trophic communities has occurred, with herbivores, omnivores, vertivores, frugivores and scavengers seeing net increases, while invertivores, granivores, nectarivores and aquatic predators have exhibited declines. We suggest that avian biologists can benefit from increased inclusion of biomass as a metric of trophic‐ and community‐level ecosystem function.