Monarch butterfly migration was off this year

Researchers are worried

“Migration conditions are a ‘Goldilocks’ sort of thing. Weather, like porridge, can be too hot, too cold or just right,” says Chip Taylor, head of the University of Kansas’s Monarch Watch. Above, a monarch butterfly lands on some swamp milkweed in an area of natural prairie at Noelridge Park Friday in Cedar Rapids in 2011. (The Gazette)
“Migration conditions are a ‘Goldilocks’ sort of thing. Weather, like porridge, can be too hot, too cold or just right,” says Chip Taylor, head of the University of Kansas’s Monarch Watch. Above, a monarch butterfly lands on some swamp milkweed in an area of natural prairie at Noelridge Park Friday in Cedar Rapids in 2011. (The Gazette)

Thanksgiving was right around the corner, and a sizable number of one of America’s most famous migrants could be seen still sputtering south. Not across the Texas-Mexico border, where most monarch butterflies should be by that time of year.

These fluttered tardily through the migratory funnel that is Cape May, N.J., their iconic orange-and-black patterns splashing against the muted green of pines frosted by the season’s first chill.

This delayed migration is not normal, and it alarmed monarch researchers nationwide. The Cape May stragglers were only a sliver of the record number of monarchs reported in the Northeast in November and December — news that sounded good initially to conservationists.

But seeing butterflies so far north so late in the year suggested that few of these latecomers would reach their Mexican wintering grounds.

Scientists fear that climate change is behind what they’re calling the latest monarch migration ever recorded in the eastern United States, and they worry that rising temperatures pose a new threat to a species that saw its population hit record lows in recent years.

“Migration conditions are a Goldilocks sort of thing. Weather, like porridge, can be too hot, too cold or just right,” said Chip Taylor, who heads the University of Kansas’s Monarch Watch, the country’s most comprehensive monarch research program.

“What a warm fall does is often delay the migration in various ways. Late monarchs just don’t get to Mexico as well as early monarchs do. The difference is quite striking.”


“A lot of people were very concerned” with the late flight, said Mark Garland, director of the Monarch Monitoring Project, which operates through New Jersey Audubon’s Cape May Bird Observatory.

‘The warmest fall’

Known for their complex, improbable migrations, most monarchs embark each fall on 2,000-mile journeys from breeding grounds as far north as Canada’s Maritime Provinces down to the Sierra Madre mountains in central Mexico. A separate western population heads mostly to southern California.

They mate in Mexico, then fly back north to lay their eggs — and die — in the spring.

Because they’re so delicate — each weighs less than a gram — monarchs are particular about flying conditions and are especially vulnerable to extreme weather systems. Major storms, high winds and early freezes pose large-scale dangers.

But more pernicious than that, scientists believe, are the warmer temperatures, probably a sign of climate change, that manipulated the monarchs’ instincts and postponed their migration.

“It was the warmest fall we’ve ever had, at least in the last 123 years,” Taylor said.

Average high temperatures in the Northeast exceeded 60 degrees in September and October for the first time, according to the National Oceanic and Atmospheric Administration.

Those temperatures are part of a 30-year trend of increasing heat that has more or less paralleled a precipitous decline in monarch populations. According to the U.S. Fish and Wildlife Service, the number of monarchs has dropped from a billion in their heyday to about 33 million in 2014 — or more than 80 percent since the mid-1990s.

In Iowa, Iowa’s State Climatologist Harry Hillaker said, “The most unusual aspect of the temperatures that we had in the warmer half of this past year was a very cool spell that we had from the last few days of July to the first few days of September. During that period, there were only a handful of days when temperatures averaged warmer than normal.


Thank you for signing up for our e-newsletter!

You should start receiving the e-newsletters within a couple days.

“Otherwise, the year as a whole was actually quite warm — in the top 10 for the state. That change of temperatures might have been a negative for the monarchs.”

“The general consensus is that the Midwest portion of the monarch population is really the main driver of the numbers that you see in Mexico,” said John Pleasants, an assistant biology professor at Iowa State University who primarily focuses his research on monarch butterfly conservation. “There are indications that the northeast population certainly has some contribution. “But if you just looked at the northeast population and tried to make some sense out of the numbers in Mexico, you would probably be way, way off. From what I saw here (in the Midwest), it wasn’t an especially good year and not an especially bad year, but sort of in between.”

Pleasants said the nectar plants that the butterflies need to get the “fuel” to get to Mexico and get fuel reserves to make it through the winter had “pooped out” by the time the northeast population began to migrate south later than normal in the year.

“You have a lot of individual monarchs that are trying to fly from the northeast to Mexico, and they are just not finding the nectar sources that they need to make it. They also could have run into bad weather and that knocks them down.”

Pleasants said he’s not expecting to see really good numbers of monarchs in Mexico — maybe two or three hectares (4.94 or 7.41 acres) — when the data is released next month.

“That’s not especially high, but it’s not the lowest we have seen,” he said.

Thousands of volunteers

For decades, scientists focused on two main causes to explain what was happening to the monarchs — loss of habitat to development in the United States and in the Mexican winter grounds, and widespread agricultural use of pesticides that destroy milkweed, their favorite plant.

The tangible nature of these threats long has helped turn monarchs into one of our most accessible and unifying symbols of conservation. Thousands of volunteers are attracted to monarch conservation efforts each year, according to the Fish and Wildlife Service, in part because of the butterflies’ aesthetic but also because the ways to help them — by planting milkweed, for example — tend to dovetail with popular hobbies such as gardening.


Saving threatened whale species requires a herculean effort in far-off and inaccessible places. Helping monarchs, for many people, means planting milkweed and then noticing if one fluttered into your living room.

“But nobody ever looks at the weather part of the system. Unless you understand the nuance created by the weather, your data will be completely full of noise,” Taylor said. And “if you look ahead to 2040 — oh, my God, you don’t want to look ahead to 2040,” given the projections for future temperature rises.

‘A huge flight’

In the autumn of 2017, things at first looked promising for monarchs. They appeared to breed well in the Northeast.

Then they arrived en masse along their Atlantic Coast flyways in substantially higher numbers than in the Midwest, where milkweed is being lost more rapidly. Don Riepe, who has counted monarchs along New York’s barrier beaches for nearly four decades, reported seeing 35,000 butterflies on Oct. 10.

“It reminded me of a huge flight in the late 1970s,” he said. “Back then, they would stream across the highway in enormous numbers. You couldn’t help but accidentally kill dozens while you drove.”

But Riepe observed this year’s flight on New York’s barrier beaches two weeks later than the butterflies normally show up there.

And along the South Carolina coast, where a little-known population winters, migrants pulsed through in unusual numbers in November, also two weeks tardy. Taylor called it the latest fall migration since Monarch Watch began tracking in 1992.

Some watchers wonder if the tardiness has another, more hopeful explanation — that the warmer temperatures this summer spawned a “bonus generation” of monarchs. In that case, even a few surviving stragglers would bolster the overall number of butterflies that made it to Mexico.


“We had our best numbers since 2012. Of course, that was skewed a little because of the late surge,” Garland said.

“But the bonus generation may have had very little success. There are always more questions than answers.”

Sometime this spring, the annual census of monarchs overwintering in Mexico will be released. The Fish and Wildlife Service will use that and other data to decide by 2019 whether monarchs warrant federal protection under the Endangered Species Act.

“Among the threats to the monarch we’re looking at is the impact of climate change,” said Georgia Parham, a spokeswoman for the service. “It’s a question all modern scientists have: How do these different factors impact now what is looking like a declining trend?”

Gazette correspondent George C. Ford contributed to this article.



Rural Iowa has struggled for decades to hang on to its residents. Even as the state's total population has grown - although slowly - most areas have seen consistent losses. "Iowa and the Midwest are losing ground competitively to ...

A man was arrested and received several charges after Marion Police officers, responding to a call complaining of possible drug activity, arrived at a residence and found a 'marijuana growing operation' in the basement of the hous ...

Give us feedback

Have you found an error or omission in our reporting? Tell us here.

Do you have a story idea we should look into? Tell us here.