VAGRANCY describes when birds veer off-course and continue roving around — potentially indefinitely — in search of others of their kind. It is not uncommon. There are records of albatrosses spending decades living as vagabond singletons in the wrong hemisphere, Dr. Lees said.

“It would be like an elephant walking up out of Africa into Scandinavia,” Mr. Lund said. “Like getting a call that the Rolling Stones are playing in a field behind a warehouse in the next town over.”

Dr. Lees said vagrancy, as a biological mechanism, could help migratory birds expand their ranges, a potential advantage as global warming redraws the contours of suitable habitat. Dr. Farnsworth said, conversely, extreme weather — which is anticipated to grow in frequency and intensity as climate change progresses — can also play a role in displacing birds by hundreds or even thousands of miles.

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