AUTHOR=Bonter David N. , Greig Emma I. TITLE=Over 30 Years of Standardized Bird Counts at Supplementary Feeding Stations in North America: A Citizen Science Data Report for Project FeederWatch JOURNAL=Frontiers in Ecology and Evolution VOLUME=9 YEAR=2021 URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2021.619682 DOI=10.3389/fevo.2021.619682 ISSN=2296-701X