固定住在一个地方不迁徙(xǐ)的鸟儿,在近距离飞行时,山峦、石头、树木都是它们确定方向的参照物。但那些根据不同季节在南北方迁徙的候鸟,靠什么确定方向呢?生物学家发现,太阳是鸟类确定方向的参照物。极地燕鸥在北极筑巢产卵,却在南极过冬,每年长途迁徙数万千米。燕鸥飞行的朝向和太阳光之间的夹角每小时改变15°。燕鸥就根据夹角的变化不断 Fixed in a place where the birds do not migrate (xǐ), at close range, the mountains, rocks, trees are their reference to determine the direction. But what are the directions for migratory birds migrating north and south depending on the season? Biologists have found that the sun is a reference for bird identification. Polar terns nest in the Arctic spawning, but winter in the Antarctic, tens of thousands of kilometers each year long-distance migration. The angle between the flight of the tern and the sunlight changes 15 ° per hour. Terns on the basis of changes in angle constantly