Butterflies Respond to Climate Change by Moving North

Part-time butterfly watchers in Massachusetts have taken more than 19,000 expeditions over the past two decades. The result of their work: northern butterflies are becoming increasingly rare, even as southern species take their place. The likely cause: warming temperatures.

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Scientists can’t be everywhere at once. Senior professors need to carve out time for teaching, lobbying for grants and even occasionally answering phone calls from annoying reporters. Grad students are often the ones who do the grunt work of science, but even they have to eat, sleep and sometimes bathe.

That’s why citizen scientists are so useful, gathering much wider sets of data—especially in the natural world—than the professionals could do alone. Take a new paper published on August 19 in the journal Nature Climate Change. Researchers at Harvard Forest—an environmental lab at Harvard University—drew on data collected by amateur Massachusetts lepidopterists, or butterfly watchers, to show that warm-climate butterflies that were once rare in the Northeastern state have become increasingly common over the past two decades. Over the same time period, more than three-quarters of once common northerly species like the atlantis and aphrodite fritillaries have become increasingly rare.

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The likely cause is the warming climate, as study lead author Greg Breed put it in a statement:  “Over the past 19 years, a warming climate has been reshaping Massachusetts butterfly communities.”

That species are responding to global warming by moving north in an effort to escape rising temperatures isn’t that surprising—other studies have indicated the growing frequency of such migrations. But the Harvard study benefits from truly granular data of butterfly movements in Massachusetts, gathered by members of the Massachusetts Butterfly Club over nearly 20,000 expeditions undertaken throughout the state. (For the same reason, scientists have a particularly good grasp on how birds have responded to warming temperatures, thanks to the meticulously kept records of amateur birdwatchers around the world.) The Massachusetts lepidoptera fanatics found, for instance, that the frosted elfin, a southern species that had long been rare in the state, has seen a 1000% increase since 1992, even as more common butterflies have disappeared—most likely to move north themselves in search of cooler temperatures, though the Nature Climate Change study only covered Massachusetts.

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The study shows that climate change is likely to through some species into unpredictable flux, but it doesn’t always mean extinction. As northerly butterflies moved out, species that were more accustomed to the warming temperatures moved in. But that flux will screw with the conservation plans of governments—Breed notes that many of the once-rare southern butterflies have habitat protection, even though they’re no longer so rare, while the once-common northern butterflies lack that protection at the very moment when they need it. That’s a major challenge for a conservation movement built around the creation of protected areas—what good is a park if the endangered species needs to move just to survive warmer temperatures? Even if those species can find escape by moving north (or south below the equator), there’s no guarantee they’ll thrive in those new environs. And eventually, they might just run out of room.

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