The Heat Is Online

Butterfly Study Confirms Warming-Driven Migrations

While previous studies documented only localized species migrations in response to atmospheric warming, an August, 1996 study in the journal Nature indicated that the entire migratory range of one type of butterfly has shifted northward in response to just a slight increase in temperature.

Following a 14-month survey of Edith’s checkerspot butterfly populations, Dr. Camille Parmesan discovered that butterfly colonies were becoming extinct at the southern end of their geographic range in Mexico and southern California while their numbers were increasingly significantly in Canada.

"What my study shows," she told the New York Times, "is that we’re apparently seeing an effect, even though this is a small warming. The effect is stronger than I expected." "When you put it together," she added, "the picture that’s coming out is that climatic warming is affecting wild organisms."

Parmesan’s butterfly study is the first that surveyed the entire geographical range of a species’ migration pattern. While other studies documented local population shifts, such as the northward migration of warm-water sea animals in the Pacific Ocean, they were too localized to show a range shift for the species as a whole. According to Parmesan, who is a researcher at the National Center for Ecological Analysis and Synthesis at the University of California at Santa Barbara, the southernmost butterfly colonies were four times more likely to be extinct than those at the northernmost latitudes.

Citation: "Western Butterfly Shifting North as Global Climate Warms," New York Times, Sept. 3, 1996; "Climate and species range," Camille Parmesan, Nature, Vol. 382, Aug. 29, 1996. See also