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As the world warms, birds are returning to warmer climes earlier in the spring.

That’s the finding of a new study that used computer vision techniques developed at the University of Massachusetts to analyze 24 years of data from National Weather Service radars and pick out flocks of birds.

The researchers found that spring migrants were likely to pass certain stops earlier now than 20 years ago.

The changes in bird migration timing were also greatest in regions warming most rapidly, researchers said.

“Decadal changes in surface temperatures predicted spring changes in migratory timing, with greater warming relating to earlier arrivals,” the study said.

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The research, led by Kyle Horton, a professor at Colorado State University, was published Monday in the journal Nature Climate Change. Co-authors included artificial intelligence researcher Dan Sheldon at UMass Amherst. The senior author was Andrew Farnsworth of the Cornell Lab of Ornithology.

The researchers believe that theirs is one of the first studies to examine climate change impact on bird migration timing on a continental scale. The research looked at nighttime migratory behavior of hundreds of species representing billions of birds, researchers said in statements from UMass and Colorado State.

“It’s not a surprise that birds’ movements track changing climates. But how assemblages of bird populations respond in an era of such rapid and extreme changes in climate has been a black box,” Farnsworth said.

Researchers at UMass opened a new window on the bird migration by designing computer vision techniques to tease out the radar traces of birds from the weather, a problem that had challenged wildlife biologists for decades.

“Historically, a person had to look at each radar image to determine whether it contained rain or birds,” said Dan Sheldon, associate professor of computer science at the University of Massachusetts Amherst. “We developed ‘MistNet,’ an artificial intelligence system to detect patterns in radar images and remove rain automatically.”

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The researchers said they accessed and analyzed the radar data through Amazon Web Services as part of the Big Data Project of the National Oceanic and Atmospheric Administration, which is the parent agency of the National Weather Service.

Horton noted that just because the birds are changing their behavior doesn’t mean they are keeping pace with climate change.

One concern is that, as climate changes, the timing of blooming vegetation and emergence of insects that birds rely on as they migrate may be out of synch with the birds. The researchers said even subtle shifts could have negative consequences for the birds’ health.

The researchers said timing shifts were less apparent in the fall. Horton said the finding was a little surprising, but migration tends to be a “a little bit messier” in the fall.

“In the spring, we see bursts of migrants, moving at a fairly rapid pace, ultimately to reach the breeding grounds,” he explained. However, during the fall, with birds not competing for mates, the birds’ paths to their destination are more relaxed.

"There’s not as much pressure to reach the wintering grounds, and migration tends to move at a slower, more punctuated pace,” he said.









Martin finucane can be reached at martin.finucane@globe.com