Scientists, politicians, and popular media frequently argue that the continued degradation of ecosystems will negatively affect human well-being. Warnings regarding the devastating consequences of ecosystem collapses have emphasized the complex interactions between natural systems, particularly how agriculture connects with surrounding ecosystems. While the potentially catastrophic costs of these events have long been theorized, empirical evidence remains scarce. The rarity of ecosystem collapses, the difficulty of clearly tracing their triggers, and the lack of detailed data pose significant barriers to rigorous empirical investigations.

Our research examines one of the most cataclysmic ecosystem collapses in history: the 1958 Four Pests Campaign (FPC) in China, which led to the local extinction of sparrows within two years. Aimed at improving agricultural productivity and public health, the FPC saw the central government ignore scientific advice and order local officials to exterminate sparrows, targeting them for eating grains. While adult sparrows do consume grains, they also feed their fledglings insects, making them important predators of crop-damaging pests. Without these sparrows, anecdotal evidence suggests that the country experienced severe crop-pest infestations. Our study provides quantitative evidence for a claim long made by environmental historians: that the local extinction of sparrows contributed to the Great Chinese Famine, in which an estimated 16.5 to 45 million people starved to death between 1959 and 1961.

The sparrow population in different parts of China was not well measured before its eradication. Our study overcomes this challenge by using ecological methods to classify counties as suitable or unsuitable for sparrows. We used newly digitized data on historical agricultural production in China to compare sparrow-suitable counties with sparrow-unsuitable counties. Our findings reveal that a county’s sparrow suitability was uncorrelated with agricultural production prior to the FPC. However, after the FPC began, sparrow-suitable counties experienced a 5.3 percent drop in rice yields and an 8.7 percent drop in wheat yields relative to sparrow-unsuitable counties for each one-standard-deviation increase in our measure of sparrow suitability. Our calculations suggest that the killing of sparrows accounts for 19.6 percent of the reduction in national crop yields during the Great Famine.

Our findings suggest two main ways in which farmers responded to the eradication of sparrows. First, the reduction in crop yields caused by the FPC primarily affected above-ground crops such as rice and wheat, which are more vulnerable to pests, especially locusts and planthoppers. In contrast, the production of below-ground crops, such as sweet potatoes, increased more in sparrow-suitable counties during this period, likely because farmers chose to switch to those crops to mitigate the risk of pests caused by the FPC. Second, sparrow-suitable counties saw marginal increases in sown areas. These effects align with the historical context: The central government permitted farmers to cultivate more land and grow sweet potatoes—exempt from mandatory procurement—to cope with the famine.

Furthermore, our research investigates the government’s response to the eradication of sparrows. Sparrow-suitable counties, despite suffering larger reductions in crop yields, faced significantly higher procurement quotas during the famine. This supports the notion that, contrary to widespread scientific advice at the time, the central government expected sparrow eradication to boost agricultural output. It also echoes prior research showing how the rigidity of the procurement system exacerbated the famine and how the government updated procurement quotas in 1958. Reduced agricultural output, combined with higher procurement quotas, placed significantly heavier burdens on sparrow-suitable counties during the Great Famine. As a result, these counties experienced increased death rates and decreased birth rates compared with sparrow-unsuitable counties. Our calculations indicate that sparrow eradication was responsible for nearly two million lives lost between 1959 and 1961.

In 1960, three years after the FPC began and following the nationwide killing of approximately two billion sparrows, the central government recognized the important role of sparrows in the ecosystem and removed them from the FPC, replacing them with bedbugs. Given that sparrows had already become locally extinct in most parts of the country, the Chinese government imported 250,000 sparrows from the Soviet Union to replenish the sparrow population, according to reports. After the sparrow eradication was reversed, rice and wheat yields returned to their original levels by 1965, and sparrow-suitable counties continued to produce more sweet potatoes. Our findings highlight the dire consequences of ecosystem collapse and indicate that the eradication of sparrows substantially contributed to the largest famine in human history.

Note
This research brief is based on Eyal G. Frank et al., “Campaigning for Extinction: Eradication of Sparrows and the Great Famine in China,” National Bureau of Economic Research Working Paper no. 34087, August 2025.