BUTTERFLY NUMBERS IN DECLINE IN AMERICAN WEST
Majority of species impacted; scientists cite climate change
Butterfly populations across the American West are declining as the region becomes hotter, drier and more vulnerable to the effects of climate change, according to a study released this month.
From California to Montana, and from New Mexico to Washington state, the populations of a majority of 450 butterfly species are dropping, according to observations by professionals and amateurs stretching back to the 1970s.
The loss of butterflies across Western forests and prairies, like the similar drop in bumblebees nationwide due to rising temperatures, is troubling because both insects play a key role in pollinating crops and wildflowers. And the findings may add to fears among researchers of a broader die-off of insects that could be under way everywhere from Germany to Puerto Rico and beyond — a potential and debated bugpocalypse that threatens to upend ecosystems across the world.
In the United States, the alarming butterfly decline is most evident in Western areas where balmy summer temperatures creep well into the fall, drying out vegetation and potentially disturbing the seasonal cycles of the fluttering insects as they prepare for cooler months.
“The influence of climate change is driving those declines, which makes sense because they’re so widespread,” said Matt Forister, a biology professor at the University of Nevada Reno and co-author of the study published in the journal Science. “It has to be something geographically pervasive.”
Scientists have long known that roadways, farms and other human development are stamping out meadows and other habitat for butterflies, while pesticides have further culled their numbers. Conservationists have taken to cordoning off areas as butterfly sanctuaries, planting vegetation such as milkweed for monarch butterflies as they migrate from Mexico across the Lower 48.
But the fact that widespread warming is weighing on such large numbers of butterflies across a vast geographic area suggests a more dire situation that cannot be abated simply by setting aside habitat. While the populations of butterfly species can vary widely from year to year, the researchers found an annual 1.6 percent drop in butterfly numbers in the Western United States over the last four decades.
Put another way: A butterfly spotter going to the same site every year saw about 25 percent fewer butterflies on average than 20 years ago.
David Wagner, an ecologist at the University of Connecticut who was not involved with the latest research, said the new findings are startling because “this is one of the first global cases of declines occurring in wildlands, away from densely populated human-dominated landscapes, and the rate of 1.6 percent is calamitous.”
The best-known butterfly on the decline in the droughtplagued region is the once-ubiquitous monarch, which used to arrive in California in such abundance every spring they regularly formed “a golden carpet” on the ground and filled the skies with “orangy” clouds, as John Steinbeck once wrote.
Now those orange itinerants are showing up in far fewer numbers. Since 1990, about 970 million monarchs have disappeared, according to a 2015 U.S. Fish and Wildlife Service report.
Others species, such as the common cabbage white butterfly and the imperiled, multicolored Edith’s checkerspot, are on downward trends, too, according to the analysis from Forister and his team.
“Rare species, common species, widespread species, local species,” said Forister, each had “detectable declines.”