The monarch butterfly is in trouble.
Each year, the monarchs head south for the winter, some making an epic journey as much as 3,000 miles long, with those in the eastern U.S. and Canada heading to forests in Mexico.
Last year, monarch reseves in Mexico saw a plummet in the number of butterflies arriving—59 percent less than the year before, marking the lowest level in 20 years.
And experts say 2013 is even worse. Gloria Tavera Alonso, director of a monarch reserve in the Mexican stae of Michoacán, told Spanish news agency EFE this week that she estimates there is a 50 percent reduction this year.
This year's loss is captured in a piece by Jim Robbins in the Sunday New York Times, The Year the Monarch Didn’t Appear:
On the first of November, when Mexicans celebrate a holiday called the Day of the Dead, some also celebrate the millions of monarch butterflies that, without fail, fly to the mountainous fir forests of central Mexico on that day. They are believed to be souls of the dead, returned.
This year, for or the first time in memory, the monarch butterflies didn’t come, at least not on the Day of the Dead. They began to straggle in a week later than usual, in record-low numbers. Last year’s low of 60 million now seems great compared with the fewer than three million that have shown up so far this year. Some experts fear that the spectacular migration could be near collapse.
“It does not look good,” said Lincoln P. Brower, a monarch expert at Sweet Briar College.
Months before, clues were in.
Asking Where Are Migratory Monarchs This Fall? Laura Tangley of the National Wildlife Federation wrote:
Each fall at about this time, I try to spend a weekend at the Black Walnut Point Inn on Maryland’s Tilghman Island in the Chesapeake Bay. Located on the southern tip of the island, the inn is a perfect place to spot large numbers of monarch butterflies stopping to feed and rest before heading across open water on their journey south to Mexico—some traveling thousands of miles from the northern United States and Canada. I time the trip according to a chart produced by Monarch Watch showing the insects’ predicted arrival dates by latitude—and I’ve not been disappointed.
Until this year, that is. Rather than the dozens of monarchs I typically see feeding by day on the inn’s asters, goldenrods and other fall-blooming plants—and the hundreds clustering for warmth on yew, holly and hackberry branches once the sun starts to go down—I spotted just a handful of monarchs in total and never more than one individual at a time.
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Like all migratory animals, monarchs, of course, are influenced by weather, and one cannot draw conclusions from a two-day visit to a single spot. Yet according to the citizen-science-fueled monitoring organization Journey North, the number of overnight monarch roosts recorded east of the Rockies this fall has been low, and roosts host fewer butterflies than in previous years. “Overall the monarch numbers in this migration are far below normal, and they are late,” says Monarch Watch founder and director Chip Taylor. “The migration in the Midwest this fall has been the lowest we have seen since the start of Monarch Watch in 1992.”
Why the low numbers? Robbins points to loss of the monarch's habitat in the U.S., fueled in part by expanding acreage for biofuels, which has included "plowing every scrap of earth that can grow a corn plant, including millions of acres of land once reserved in a federal program for conservation purposes." And increasing crop land means milkweed, the host plant for the monarch catterpillar, is wiped out, explains Laura Chisholm of the Butterfly House at the Missouri Botanical Garden.
The loss of milkweed, Tangley writes, "is particularly acute in the U.S. Midwest, where genetically engineered, herbicide-tolerant corn and soybeans now allow farmers to apply the chemicals broadly, wiping out milkweed that once thrived between crop rows and in fallow fields on millions of acres of agricultural land."
Robbins also points to the notorious but widely used herbicice Roundup, "a herbicide that kills virtually all plants except crops that are genetically modified to survive it."
Climate change is also a contributing factor. ThinkProgress reported that a
study found climate change could affect the migration of monarch butterflies, which migrate from Mexico to the southern U.S. when weather gets warm, where they lay their eggs. The study found that monarchs needed a cold trigger in order to continue migrating south to Mexico in the fall — without those cold conditions, monarchs in the midst of migrating south can actually reorient themselves and fly north.
“How many days of the low temperature are needed or the actual temperatures themselves are just not known. All we know is that for 24 days, day and night, if we mimic temperatures in Mexico, on top of the mountains there, the butterflies then start traveling north,” author Steven Reppert said.
Extreme weather could also pose a major threat to monarchs. in 2002, a severe storm in Mexico killed nearly 80 percent of the monarch butterfly population there.
“That was a very extreme and unusual weather event. It’s usually the dry season; there aren’t big storms there, but they just had a lot of precipitation. That was followed by cold temperatures, so that juxtaposition of precipitation and cold just killed all the butterflies,” Karen Oberhauser, a professor in the Department of Fisheries, Wildlife and Conservation Biology at the University of Minnesota told ClimateWire. “Clearly, that kind of storm is predicted to be more common under climate change scenarios.”
For Taylor, the outlook for the iconic monarch isn't good.
“We had some really robust Monarch butterfly populations in the 90s,” he said. “But we’re never going to see those again.”