Shapiro compared the decline of the butterflies to similar declines in populations of frogs and other amphibians. While there may be different possible explanations for declines at each location, "the pattern is regional," he said. Shapiro is working to test various ideas about why these butterflies are in decline, including combinations of changing climate and changing land use.
In the short term, he said, butterfly species that breed several times a year may rebound quickly to take advantage of improving conditions. But for species with only one brood per year, a catastrophic season will have repercussions for up to a decade.
More butterflies may still emerge in the mountains. The rain has led to a heavy snow pack in the Sierra Nevada, which typically means a good year for butterflies in the high country. Snow protects the dormant insects from cold and drying. But the snow came late in the season, meaning that many of the overwintering insects may have been killed off early. We will not know about the fate of those butterflies until July, Shapiro said.