十万个为什么·科学启蒙30篇（2）
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Why Do Birds Migrate Thousands of Miles Each Year?
为什么鸟类每年要迁徙数千英里？
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Birds migrate to find better food, warmer weather, and safe nesting places.鸟类迁徙是为了寻找更丰富的食物、更温暖的气候和安全的筑巢地。
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They use the sun, stars, Earth’s magnetic field, and even landmarks to navigate.它们利用太阳、星星、地球磁场，甚至地标来导航。
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Young birds often follow experienced adults on their first long journey south.幼鸟首次长途南迁时，常跟随有经验的成鸟。
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Some species, like the Arctic Tern, fly over 40,000 miles round-trip each year.有些鸟类（如北极燕鸥）每年往返飞行超4万公里。
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Their bodies prepare for migration by storing extra fat as fuel for long flights.迁徙前，鸟类会储存额外脂肪，为长途飞行提供能量。
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Scientists track migrating birds using tiny GPS tags attached to their backs.科学家在鸟背部安装微型GPS标签追踪其迁徙路线。
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Changes in daylight length trigger hormonal shifts that begin migration behavior.日照时长变化会引发激素变化，从而启动迁徙行为。
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Not all birds migrate—some stay year-round if food and shelter remain available.并非所有鸟类都迁徙——若食物和栖息地全年充足，一些鸟会留居原地。
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Wind patterns and weather fronts strongly influence when and how high birds fly.风向和天气系统显著影响鸟类的起飞时机和飞行高度。
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Conservation efforts protect stopover habitats where tired birds rest and refuel.保护行动致力于维护中转栖息地，供疲惫的鸟类休息和补充能量。