News Release 

Climate warming drives butterfly decline in American west, study using citizen science data shows

American Association for the Advancement of Science

Research News

Slowly warming autumn months have driven population declines in butterflies throughout the American West for the last 40 years, according to a new study, which leveraged data collected by both expert and citizen scientists. The findings shed new light on the insidious impacts of climate change on butterfly populations and suggest the need for new approaches to butterfly conservation. "Society should not assume that legal protection of open spaces is sufficient without the action to limit the advance of anthropogenic climate change," write the authors. Although alarming and widespread reductions in insect abundance and diversity have been observed over the last several decades, the recent and rapid declines in pollinator species are particularly concerning. Tiny pollinators like bumblebees and butterflies are vital to the long-term survival of wild and agricultural plant communities. They are, in many ways, critical to the integrity of biodiversity, global food webs and human health. While climate change is presumed to be a key factor in pollinator decline, the particular impacts remain uncertain and difficult to unravel from the compounding effects of other pervasive stressors, like habitat loss or pesticide use. Matthew Forister and colleagues address this challenge by combining three datasets of butterfly observations collected by experts and community scientists - the Shapiro transect, the North American Butterfly Association and the iNaturalist web platform. In total, the data encompassed more than 450 species of butterflies across more than 70 locations spanning the western United States and allowed Forister et al. to evaluate the effects of climate change-related warming and drying on butterflies across a variety of land-use gradients, from major cities to protected national parks. They also evaluated the impacts of climate-related changes on different elevational and latitudinal gradients that represent a wide range of habitat and climatic diversity. The results revealed a 1.6% annual reduction in butterfly abundance over the past four decades. While the authors note that the drivers of this decline are complex and multifaceted, they found that climate change - particularly warmer autumn months - explains a large proportion of the observed population declines for many butterflies. This study involved efforts by citizen scientists. Among the authors of this study, citizen science-driven results have been a focus for some time. Jeff Glassberg, head of the North American Butterfly Association, runs a number of community science and volunteer projects, including several planned for the near future. Reporters interested in these activities could reach Dr. Glassberg at Author Katy Prudic works with community science efforts involving crowd-sourced butterfly observations as well, specifically through the eButterfly program, an online database of butterfly observations across North America. She can be reached at


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