Extreme uncertainty and unquantifiable bias do not inform population sizes

Species-specific population estimates are fundamental for many aspects of ecology, evolution, and conservation, yet they are lacking for most species. Aiming to fill this gap, Callaghan et al. (1) estimated global bird population sizes by modeling the relationship between eBird reporting rates and independent estimates and extrapolating globally. While we applaud their intention, we caution that their modeling framework is prone to yield extremely uncertain and biased estimates that cannot support robust inferences about species abundance distributions or other applications in ecology, evolution, or conservation.