How do large disruptions to ecosystems affect human well-being? In 1958, China embarked on the “Four Pests Campaign” that aimed to quickly eradicate flies, mosquitoes, rats, and sparrows nationwide, despite warnings from scientists that sparrows play important roles in pest control. Historians have long suspected that eradicating sparrows, by letting other pest populations grow out of control, contributed to the Great Famine in China between 1959 and 1961—the largest in human history. This paper combines newly digitized data on historical agricultural productivity in China with habitat suitability modeling methods in ecology to quantitatively test this hypothesis. We document that regions with higher “sparrow suitability” experienced significant drops in agricultural output after the Four Pests Campaign, as compared to their low-suitability counterparts, which could explain a 3.1% additional drop in rice output and a 1.5% additional decline in wheat output.