BySarah Gibbens
Photographs ByGreg Kahn
Published July 28, 2023
• 9 min read
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.
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.
Exactly how the veeries’ “predict” hurricane seasons may result from small changes in regular, global cycles like El Niño and La Niña events.
(Learn more about El Niños and what it will mean for this year’s weather.)
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.
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.
“It’s a fascinating [study],” says Andrew Farnswoth, an expert in bird migrations at the Cornell Lab of Ornithology who was not involved with this research. Farnsworth was not familiar with any studies showing similar correlations, but he says Heckscher’s study is logically sound.
“The fact that there’s an interesting pattern like this, it absolutely makes sense,” he says. “There are a whole load of connected events, a sort of butterfly effect.”
Climate change upsets a delicate balance
Migrations like the ones taken by the veeries have formed over thousands of years as birds sense and react to predictable changes in the weather.
“The issue now is the speed with which the climate is changing. Can birds respond quickly enough?,” says Farnsworth.
Research has shown that climate change will make hurricanes more likely grow from small storms to large storms, all while marching across the ocean at a slower pace.
Heckscher worries that if hurricanes move more slowly over the Gulf of Mexico, it could mean more migrating birds like the veeries face a longer period of risk of being blown off track or killed.
(Even wildfire smoke affects birds—here’s how you can help.)
Since 1966, veery thrush populations have declined globally by nearly a third. Their South American habitat is quickly being destroyed to make room for agriculture, and their northern habitats are increasingly being fragmented.
Migratory birds like veeries also face a higher risk of colliding with buildings—every year, as many as a billion birds die as the result of flying into buildings whose glassy, reflective windows birds often mistake for open air.
It puts the veeries at risk of disappearing from forests and taking with them their chirping, melodic bird songs.
“I’m pretty concerned about these birds,” says Hecksher. “They’re vulnerable for a lot of reasons.”
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