It’s summer, and veery thrush birds have nearly finished mating and hatching this year’s generation throughout the northern U.S. and southern Canada. Soon, the brown-feathered, white-bellied bird will make a monumental move, migrating thousands of miles south—across the Gulf of Mexico and the Caribbean Sea—to South America.

It’s a dangerous journey for a small songbird only weighing about 30 grams, and if a hurricane happens to transect that migration, some of those birds may never make it.

But every hurricane season is different, and veeries, research shows, have plugged into the global climate cycles that allow them to anticipate how dangerous a season will be.

A study published in the journal Scientific Reports in 2018 showed that for two decades, veery migration patterns from Delaware to South America accurately predicted the intensity of the Atlantic Basin hurricane season. During bad years, the birds would wrap up their breeding season sooner and head down to South America early, and during mild years, the birds hung out in eastern North America for longer.

 “Hurricanes occur at the same time they’re migrating. If they end breeding season early, they can get down there sooner. It makes sense that they would figure it out somehow,” says study leader Christopher Heckscher, an ecologist at Delaware State University.

A catbird is placed in a cloth bag where it waits to be examined and tagged by scientists. At White Clay Creek State Park in Delaware, Heckscher and his research team study the migration habits of local birds. Every year, many species journey thousands of miles south for the winter.

Graduate student Tahira Mohyuddin pull a veery from ​a net used to catch the birds. When a hurricane season is expected to be especially dangerous, veeries finish their ​nesting season early, molt a fresh set of feathers, and fly south ​before the peak of the season strikes.

Veeries are small birds, weighing anywhere between 20 and 50 grams. One theory for how their predict hurricanes: when more rain falls in their South American habitat, more fruit is available, making them fitter and more capable of staying in North America for longer.

A close-up of a veery wing, which can indicate the bird’s age. For more than two decades, the team of researchers at Delaware State University has been logging data on local birds, insights that provide clues to Earth’s inner workings.

Since Heckscher’s study published, the birds have continued to figure it out. While he says it’s too early to determine what the birds are predicting for 2023, in three of the last four Atlantic hurricane seasons, veeries have been just as accurate, and in one case more accurate, than meteorological models.

“These birds are taking a cue from somewhere, and it could be something we haven’t discovered yet,” Heckscher says.

And while he hasn’t looked for similar patterns among other migratory birds, he suspects they exist.

A lot of research has gone into studying bird migration at the animals’ rest stops, like the Gulf of Mexico, he says. “If we were to look for this predictive hurricane signal in that data, I think we would probably find it.”

How veeries predict the future

Heckscher thinks the birds get their meteorological intel from their wintering grounds in South America, where the large-scale weather patterns that influence hurricane seasons unfold long before a hurricane forms.

Heckscher has been studying veeries for 25 years, and his discovery that their migration patterns and hurricane seasons were linked, came by accident when he noticed the birds’ habits changed from year to year. “I thought, well, hurricanes occur at the same times they’re migrating, maybe if they end breeding season early they can get down there sooner.”

Exactly how the veeries’ “predict” hurricane seasons may result from small changes in regular, global cycles like El Niño and La Niña events.

During El Niño years, the Pacific Ocean water is warmer than average, and those same Pacific Ocean temperatures produce winds that more effectively tear apart hurricanes, leading to below average hurricane seasons. The inverse is true for a La Niña year. With these seasonal changes, rainfall in veery habitat may vary, and during years when more rain falls, more fruit could be available, a major staple in the veeries’ diet.

The result of these rainfall fluctuations happening 5,000 miles away: a reliable prediction for hurricane season.

Heckscher hypothesizes that this change in diet may help the veery return to North America in better shape, more capable of a longer breeding season. Conversely, with too little fruit, they may be driven by their lack of physical fitness to cut their breeding season short.

“Something is happening in their blood chemistry or hormones that’s causing them to stop breeding at a certain time,” says Heckscher.

A wood thrush, a bird slightly larger than a veery thrush, is caught an analyzed by researchers. Like the veery, a wood thrush migrates south every year and spends its fall and winter in Central America.

The catbird, like its thrush neighbors, leaves its North American spring and summer breeding grounds to spend the cold fall and winter months in Central and South America. 

Cardinals, like the female being studied here, are found in eastern and central North America. Unlike veeries, they don’t migrate. Their distinct red feathers and head shape make them a favorite among bird watchers. 

The ovenbird here is a type of warbler. It breeds in the eastern U.S. and southern Canada before flying south to the Caribbean and Mexico for the winter. Birds, both the ones that migrate and those that stay p…Read More

For his study, he and his colleagues observed birds from 1998 to 2016, and almost every year, the veeries’ behavior was an accurate indication of whether hurricane activity in the U.S. would be below or above average.