These songbirds seem eerily good at predicting hurricane seasons, Delaware researcher finds

WILMINGTON, Del. – This year, a little bird signaled a Delaware researcher that the 2019 tropical storm season in the Atlantic Ocean was going to be more active than normal.

“If you think about it, it makes a lot of sense,” said Christopher Heckscher of Delaware State University, who found the link between veery thrushes and tropical storm activity.

“These birds have evolved in concert with storms in the fall, during their migratory period for, theoretically, thousands of years if not more. It would make sense that they would, at some point, get in sync with the climate at a larger global scale.”

For two decades, Heckscher has been studying Delaware’s densest population of veery thrushes, a cinnamon-colored songbird with a spotted chest that migrates every spring from the southern Amazon basin to northern breeding grounds that stretch from Delaware to Canada. 

Over the years he has watched and tracked one population of veeries nestling into the forests of White Clay Creek State Park each spring. Even though the species travels thousands of miles for this moment, they only ever raise one clutch, or one successful nest of usually two to four chicks.

“I started to notice that in some years the birds were stopping their breeding season earlier than other years,” the ornithologist, entomologist and environmental science professor said.

He began to wonder why after a few years of shorter breeding seasons. Did they not have enough food? Was it because the weather was too dry or too hot?

Eventually, he started looking at what advantage the birds would have by shortening their nesting season. That’s when he thought to look at tropical storm activity, which occurs along their long migratory route.

“It turns out that in years they stop breeding earlier, there’s more tropical storm activity on their migration route,” Heckscher said. “I thought of that idea, I tested the hypothesis, I looked at the data, but I really wasn’t expecting there to be any relationship there.

“And it was a really strong relationship.”

Nearly 20 years of data showed Heckscher that not only does the length of the veery’s breeding season relate to future tropical storm activity, but the average number of eggs in each nest could also signal whether the season will be normal, slow or overly active. He found that females produce more eggs when an active hurricane season is in store.

“The chances of this relationship being coincidental, in my opinion, are pretty small,” he said. “We don’t know for sure that the relationship is real, but there is a relationship between what the birds are doing and the following tropical storm season.”

In late May, NOAA predicted that this year’s Atlantic tropical storm season, which lasts from June 1 to Nov. 30, would be near normal. It called for up to 15 named storms, two to four of which would become major hurricanes.

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Meanwhile, the veery thrush data from this spring indicated the season would be a bit more active than normal.

By their next update in August, NOAA changed its prediction for the season and increased the chances of an above-normal season with up to 17 named storms. As of Nov. 1, there have been 17 named storms and three major hurricanes.

The birds had it right all along.

“Which is pretty incredible if you think about it because these birds, the timing of their breeding season is determined in May and June, and that storm activity is happening in September, October, November,” Heckscher said.

Last year, Heckscher published a paper on his songbird and hurricane findings, but the data has yet to be used in NOAA’s forecasting. That won’t happen until researchers such as Heckscher can find some missing puzzle pieces.

His research also will be featured in a Netflix documentary expected to come out next year, he said.

While the link between these thrushes and tropical activity is clear, he said, it remains a mystery how the thrushes are able to sense future weather patterns as accurately or better than advanced meteorological super computers.

Heckscher has a few guesses, but it will take more of research and studies to pinpoint how the birds are able to predict weather patterns for their own safety, and whether other migratory species are able to do the same.

He said there’s a possibility that the birds can somehow sense sea-surface temperatures – a huge factor in hurricane development and strength, on their journey north. Or that maybe precipitation or other environmental factors in their wintering grounds could be providing cues that humans haven’t yet picked up on. 

“Whatever it is, it’s something that they’ve already figured it out by mid-May at the latest, really,” he said. “It’s just opened up so many other questions. How do they know this?”

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How NOAA predicts tropical storm seasons

Until researchers can figure out how the veeries predict future weather patterns, public safety relies on the modeling and forecasting provided by federal agencies.

Even after decades of fine-tuning, there always remains a certain level of uncertainty in forecasts, said meteorologist Matthew Rosencrats with NOAA’s Climate Prediction Center.

NOAA uses a combination of what experts call statistical and dynamical tools, which look at patterns of sea-surface temperatures and upper level winds, as well as computer modeling, to help predict how many tropical storm systems could develop months in advance.

Those forecasts are delivered in July and again in August for a season that peaks around Sept. 10, he said.

While Rosencrats said he hasn’t seen Heckscher’s study and data, and researchers would have to pinpoint the physical and biochemical bases that drive the veery’s ability to forecast tropical storms before it could be helpful in a more public way.

“If we could ever figure out the biological and statistical reasoning why, it could be used,” he said. “The wildlife of Delmarva, they’re really important to the whole ecology of the region, to the economy and to tourism.”

Follow reporter Maddy Lauria on Twitter @MaddyinMilford.