After cross-equatorial wintering, migratory birds reliably return to their natal grounds, but a population of cliff swallows recently switched breeding hemisphere. They inverted their annual cycle and migration directions almost instantaneously.

中文翻译：

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鸟类迁徙：时钟和指南针促进半球切换

在跨赤道越冬后，候鸟可靠地返回它们的出生地，但最近一群悬崖燕子改变了繁殖半球。他们几乎在瞬间反转了他们的年度周期和迁移方向。