North American bird declines are greatest where species are most abundant

Efforts to address declines of North American birds have been constrained by limited availability of fine-scale information about population change. Using participatory science data from eBird, we estimated continental population change and relative abundance at 27 km resolution for 495 bird species from 2007-2021. Results reveal high and previously undetected spatial heterogeneity in trends; although 75% of species were declining, 97% of species showed separate areas of significantly increasing and decreasing populations. Populations tended to decline most steeply in strongholds where species were most abundant, yet they fared better where species were least abundant. These high-resolution trends improve our ability to understand population dynamics, prioritize recovery efforts, and guide conservation at a time when action is urgently needed.