迁徙的鸟布满了灰白的天空。
燕子在冬天迁徙到南方。
大多数的鸟类不得不飞行很长的距离进行迁徙。
现在，迁徙是一种自然的生存策略。
它导致大量企鹅和鲸鱼迁徙。
它们导致一些鸟类放弃迁徙。
不冬眠的一个补偿方式是天生的迁徙习性。
One compensation for not hibernating is the built-in urge to migrate.
在晚上迁徙的鸟呢？
为什么会发生野生动物濒临灭绝和迁徙的现象？
Why did the near extinction and migrations of wild animals occur?
然而，人类行为正在对动物迁徙产生不利的影响。
Human behaviour, however, is having a detrimental impact on animal migration.
一种观点认为，这些画是兽群季节性迁徙的记录。
One opinion is that the paintings were a record of seasonal migrations made by herds.
无需人工帮助的物种迁徙也只能维持几个月的时间。
There are a few quarters left for species to migrate through without help.
磷虾数量的减少和气温的升高可能迫使南极鲸迁徙。
Shrinking krill population and rising temperatures could force Antarctic whales to migrate.
无论如何定义，动物迁徙都远远不止是动物的移动。
Animal migration, however it is defined, is far more than just the movement of animals.
北美和南美的物种迁徙穿过地峡，现在开始互相竞争。
North and South American species migrating across the Isthmus now came into competition with each other.
鸟类在长途迁徙飞行之前，会用大量的食物喂肥自己。
Birds will fatten themselves with heavy feeding in advance of a long migrational flight.
他们使从南方迁徙过来的波斯瞪羚的后代可以生存下去。
They subsisted offspring migrations of Persian gazelles from the south.
鲑鱼在河流和海洋之间迁徙时也会携带危险的化学物质。
Salmon also carry dangerous chemicals as the fish migrate between rivers and the sea.
某些海鸟在每年春季迁徙到北方繁殖地时，以这些鸟蛋为食。
Certain shorebirds depend on these eggs for food during their annual spring migration to their northern breeding grounds.
动物在寒冷的冬天有三种主要的生存方式：休眠、适应或迁徙。
There are three main ways that animals survive the cold in winter: sleep, adapt or migrate.
当然，有些动物物种需要大面积的栖息地，有些则需要长途迁徙。
There are, of course, animal species that require large areas of habitat, and some migrate over very long distances.
有些鸟会飞到更温暖的地方迁徙过冬，在那里可以找到更多食物。
Some birds migrate by flying to a warmer place for the winter, where they can find more food.
当旅鼠的食物供应不足以维持种群时，一次特别的迁徙就开始了。
When the lemmings' food supply becomes too low to support the population, a singular migration commences.
除非有确凿的考古证据支持，否则我们应谨慎对待给出的迁徙日期。
Dates given for the migrations should nevertheless be treated with caution, except where supported by hard archaeological evidence.
它们阻止了鱼类迁徙，并改变了对本地物种至关重要的水生栖息地。
They prevent fish migrations and change aquatic habitats essential for native species.
岩石艺术让我们得知人类的迁徙：人们从哪里来，接下来可能去哪里。
Rock art tells us about migration: where people came from and where, perhaps, they went next.
他的定义比伯杰的更复杂，加入了区分迁徙与其他运动形式的五个特征。
His definition is more intricate than Berger's, citing those five features that distinguish migration from other forms of movement.
我们需要智慧和决心，以确保迁徙的物种能够在更长时间里继续它们的旅程。
We will require wisdom and resoluteness to ensure that migrating species can continue their journeying a while longer.
我们不能把植物给忘了，没有它们事先入侵陆地，就不会有其他的迁徙发生。
We mustn't forget the plants, without whose prior invasion of the land none of the other migrations could have happened.
对牙齿的分析还表明，纳-德内人和爱斯基摩-阿留申人后来还有过两次迁徙。
Tooth analyses also suggest that there were two later migrations of Na-Denes and Eskimo-Aleut.
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