Humans aren't the only species to rapidly adapt to urban hustle and bustle. A new study reveals that when European blackbirds (Turdus merula) move from their native forest into the city, they migrate shorter distances than their country cousins—a behavioral change that could eventually split the populations into separate species. Researchers studied 168 blackbirds along a 2800-kilometer path in and around seven cities from Spain to Estonia. When blackbirds eat and drink throughout Europe, different atomic varieties of hydrogen become incorporated into their beaks and feathers, which give clues to their migration patterns. The data revealed that urban blackbirds in northern Europe, which started moving into cities in the 1930s, stay closest to home during the winter. Meanwhile, their forest-dwelling counterparts still take to the wing each year for warmer climes, traveling to southern Europe or as far as northern Africa, the team reports online this month in Oikos. Cities tend to stay warmer than the countryside and there's lots of food within easy reach -- factors that may keep urban birds lazing about town. The migratory divide could explain genetic differences that have already arisen among the urban and rural blackbird populations -- a possible first step to a species split.
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