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Crows have consistent habits of partial migration, study shows

"Personally, I find the sight of an 8,000-crow roost exhilarating," said researcher researcher Andrea Townsend.

By
Brooks Hays
Satellite trackers allowed scientists to follow the migrational patterns of American crows across several seasons. Photo by M. Jones/American Ornithological Society
Satellite trackers allowed scientists to follow the migrational patterns of American crows across several seasons. Photo by M. Jones/American Ornithological Society

Aug. 8 (UPI) -- In many parts of North America, crows seem omnipresent. But while many crows stay in the same place all year, others migrate.

New research has offered fresh insight into the phenomenon of "partial migration" among crows.

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Researchers at Cornell University and Hamilton College tagged dozens of crows from winter flocks in Utica, New York, and Davis, California. The satellite tracking devices allowed scientists to monitor the crows' movements of the course of several years.

The data showed 86 percent of eastern crows and 73 percent of western crows migrated to breed. The birds migrated an average of 310 miles.

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Scientists found the same crows returned to the same breeding locations, year after year. Crows that migrated one year also migrated the next, while crows that stayed put remained homebodies, year after year.

Though the data suggested consistency, scientists found evidence that crows were flexible in where they spent winters. The findings -- published this week in the journal The Auk: Ornithological Advances -- suggest crows are capable of adapting to environment shifts.

As temperatures warm, or as urban heat island effects become more pronounced, scientists predict crows will shorten their migration treks.

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Previous studies have shown global warming has already begun to shift seasonal patterns, impacting the behaviors and movements of birds and other animals.

"If you live in a place, usually a city, with a huge winter flock of crows, you are seeing migratory birds that came south for the winter as well as your local, year-round crows," Hamilton researcher Andrea Townsend said in a news release. "Personally, I find the sight of an 8,000-crow roost exhilarating, but if they or their feces are driving you crazy, you can at least take comfort in knowing that most of them will disappear in early March."

Because partial migration is a trait shared by many animals, scientists hope the research will lead to new insights into the evolution and ecology of other species.

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