Before you kill off all the sparrows, get information on what they eat and what will happen when there are no sparrows to eat whatever that turns out to be. It might for instance be insects. Think about that for a second.

Keystone species like bats and vultures have been found to play an important role in human wellbeing. A new study provides similar evidence of the role of sparrows. The study finds that the sparrows’ collapse helped to incite China’s Great Famine—the world’s most deadly famine, which led to tens of millions of people dying of starvation between 1959 and 1961.

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The Chinese government targeted the sparrow for eradication in 1958 because they believed the birds were eating crops—though scientists warned the government that the birds also eat crop-eating insects. The government ignored scientific advice and successfully drove sparrows to local extinction within two years. Frank and his co-authors—Shaoda Wang also of UChicago, Qinyun Wang of Fudan University, Xuebin Wang of Shanghai University, and Yang You of the University of Hong Kong—provide the first quantitative evidence to back up long-held beliefs that the sparrows’ collapse played a role in forming the conditions that gave rise to the Great Chinese Famine.

Frank and Wang compared crop productivity and mortality rates in counties that had more sparrows to counties that had less sparrows before and after the birds were targeted. They find that rice and wheat crops—more vulnerable to insects like locusts because they grow above ground—declined by 5 percent and 8 percent, respectively, in counties more impacted by the killing of the sparrows. Meanwhile, sweet potato crops—grown below ground—flourished in more impacted counties because they were less vulnerable to insects likely on the rise in these areas.

“During this time, the government began to require farmers to sell more of their crops because they believed the sparrow eradication had boosted agricultural production,” says Yang You, an assistant professor at the University of Hong Kong’s Business School. “The opposite was true. These counties that were suffering the most severe crop losses, had even less food, and the famine worsened. That could have been avoided if the government had listened to scientists.”