72 The Migration of Birds

Birds are lucky. They can chirp, “I have wings. Will travel.” Birds migrate for various reasons. But mainly it is the food supply.

How do birds find their way? A partial answer: They follow such landmarks as coastlines. Some birds fly inland routes. Perhaps they follow rivers or mountain ranges. But some birds fly only at night. Then landmarks are of little use. There is still much to learn about migration.

Great distances are covered during migrations. The arctic tern holds the record. It flies 22,000 miles round-trip. It leaves the Arctic Circle in late August. Its destination is the Antarctic Circle. Later, the terns fly north. They arrive at the Arctic Circle about mid-June.

The term may hold the record, but the bobolink is competing. Bobolinks fly in one big flock. Their route is called the bobolink route. Few other birds ever use it. Flying only at night, they leave the island of Jamaica and fly 500 miles over the ocean to Mexico.

But the hummingbird is the real wonder bird. It may fly from the eastern United States over the Gulf of Mexico to the Yucatan in Mexico. How can such a small bird have enough energy to fly such a distance nonstop? This bird is the smallest and daintiest one in the U.S. It is less than four inches long. It lives on nectar from flowers. This nectar provides the power to its wings. The wings move about 60 to 70 times a second (not minutes). You can be sure of this: there are no fuel-refueling stations on the gulf. There are no islands. Some speculate the birds get into air currents. But nobody really knows. It’s a mystery. It’s a wonder. It’s good to still have wonders.

鸟类很幸运，它们可以鸣叫：“我有翅膀，我要旅行。”鸟类迁徙有多种原因，但主要是为了食物供应。

鸟类是如何找到路的？部分答案是：它们会沿着海岸线等地标飞行。有些鸟类走内陆路线，也许它们沿着河流或山脉飞行。但有些鸟类只在夜间飞行，那时地标几乎派不上用场。关于迁徙，还有很多有待了解的地方。

迁徙过程中鸟类会跨越很长的距离。北极燕鸥保持着纪录，它往返飞行2.2万英里。它在八月下旬离开北极圈，目的地是南极圈。之后，燕鸥向北飞行，大约在六月中旬抵达北极圈。

北极燕鸥可能保持着纪录，但食米鸟也在竞争。食米鸟成群飞行，它们的路线被称为食米鸟路线，很少有其他鸟类使用这条路线。它们只在夜间飞行，离开牙买加岛，飞越500英里的海洋前往墨西哥。

但蜂鸟才是真正的奇鸟。它可能从美国东部飞越墨西哥湾到墨西哥的尤卡坦半岛。这么小的鸟怎么有足够的能量不间断飞行这么远的距离呢？这种鸟是美国最小、最娇美的鸟，体长不足4英寸，以花蜜为食，花蜜为它的翅膀提供动力，翅膀每秒振动约60到70次（不是每分钟）。可以肯定的是，墨西哥湾没有加油站，也没有岛屿。有人推测鸟类借助气流飞行，但没人真正知道，这是个谜，是个奇迹，幸好还有奇迹存在。