第1段

Animal migration, however it is defined, is far more than just the movement of animals. It can loosely be described as travel that takes place at regular intervals – often in an annual cycle – that may involve many members of a species, and is rewarded only after a long journey. It suggests inherited instinct. The biologist Hugh Dingle has identified five characteristics that apply, in varying degrees and combinations, to all migrations. They are prolonged movements that carry animals outside familiar habitats; they tend to be linear, not zigzaggy; they involve special behaviours concerning preparation (such as overfeeding) and arrival; they demand special allocations of energy. And one more: migrating animals maintain an intense attentiveness to the greater mission, which keeps them undistracted by temptations and undeterred by challenges that would turn other animals aside.

动物迁徙，不管如何定义，远不止是动物的运动。它可以粗略地描述为定期发生的旅行-通常是在一年周期内-可能涉及物种的许多成员，并且只有在长途旅行后才获得奖励。它表明了遗传本能。生物学家休·丁格尔已经确定了适用于所有迁徙的五个特征，这些特征在不同程度和组合上适用于所有迁徙。它们是使动物离开熟悉栖息地的长时间移动；它们倾向于是线性的，而不是曲折的；它们涉及有关准备（如过度进食）和到达的特殊行为；们需要特殊的能分配。还有一个：迁徙动物保持对大使命的高度专注，这使它们不受诱惑的干扰，也不受其他动物会转向的挑战的阻碍。

第2段

An arctic tern, on its 20,000 km flight from the extreme south of South America to the Arctic circle, will take no notice of a nice smelly herring offered from a bird-watcher’s boat along the way. While local gulls will dive voraciously for such handouts, the tern flies on. Why? The arctic tern resists distraction because it is driven at that moment by an instinctive sense of something we humans find admirable: larger purpose. In other words, it is determined to reach its destination. The bird senses that it can eat, rest and mate later. Right now it is totally focused on the journey; its undivided intent is arrival. Reaching some gravelly coastline in the Arctic, upon which other arctic terns have converged, will serve its larger purpose as shaped by evolution: finding a place, a time, and a set of circumstances in which it can successfully hatch and rear offspring.

北极燕鸥从南美的极端南部飞行到北极圈，全程2万公里，它不会注意到鸟类观察者在途中提供给它的美味的鲱鱼。而当地的海鸥会贪婪地俯冲接受这些馈赠，而北极燕鸥则继续飞行。为什么呢？北极燕鸥抵制诱惑，因为它在那一刻受到一种我们人类所赞赏的本能感的驱使：更的目的。换句话说，它决心要达到目的地。这只鸟意识到它可以后再进食、休息和交配。现在它全专注于旅程；它的全部图都在到达目的地。到达北极的一些卵石海岸，其他北极燕鸥也会聚集在那里，这对它的更大目的产生了影响，这是通过进化塑造出来的：到一个地方、一个时间和一组情况，以便成功地孵化和抚养后代。

第3段

But migration is a complex issue, and biologists define it differently, depending in part on what sorts of animals they study. Joel Berger, of the University of Montana, who works on the American pronghorn and other large terrestrial mammals, prefers what he calls a simple, practical definition suited to his beasts: ‘movements from a seasonal home area away to another home area and back again’. Generally the reason for such seasonal back-and-forth movement is to seek resources that aren’t available within a single area year-round.

但徙是一个复杂问题，生物学家们对其定义有不同的看法，部分取决于他们研究的动物种类蒙大拿大学的约尔·伯格研究美洲羚羊和其他大型陆生动物，他更喜欢称之为简单实用的定义，适合他的动物：“一个季节性的家庭区域到另一个家庭区域再返回的移动”。通常这种来回的季节性移动是为了寻找全年无法在一个地区内获得的资源。

第4段

But daily vertical movements by zooplankton in the ocean – upward by night to seek food, downward by day to escape predators – can also be considered migration. So can the movement of aphids when, having depleted the young leaves on one food plant, their offspring then fly onward to a different host plant, with no one aphid ever returning to where it started.

在海洋中，浮游动物的日常垂直运动-夜间升以寻找食物，白天下降以逃避捕食者-也可以被视为迁徙。当蚜虫在一棵食物植物上吃光了幼叶后，它们的后代会飞向另一种寄主植物，没有一只蚜虫会回到起始地点。

第5段

Dingle is an evolutionary biologist who studies insects. His definition is more intricate than Berger’s, citing those five features that distinguish migration from other forms of movement. They allow for the fact that, for example, aphids will become sensitive to blue light (from the sky) when it’s time for takeoff on their big journey, and sensitive to yellow light (reflected from tender young leaves) when it’s appropriate to land. Birds will fatten themselves with heavy feeding in advance of a long migrational flight. The value of his definition, Dingle argues, is that it focuses attention on what the phenomenon of wildebeest migration shares with the phenomenon of the aphids, and therefore helps guide researchers towards understanding how evolution has produced them all.

丁格尔是一位研究昆虫的进化生物学家。他的定义比伯格的更为复杂，引用了那五个特征，这些特征区分了迁徙与其他形式的运动。这些特征允许例如蚜虫会在远行起飞时变得对蓝光（来自天空）敏感，并且在适当时会对黄光（从嫩叶反射出的光）敏感。鸟类会在长途迁徙飞行前进行大量进食来储备能量。丁格尔争辩说，他定义的价值在于它将注意力集中在角马迁徙现象与蚜虫迁徙现象的共同点上，因此有助于指导研究人员了解进化是如何产生它的。

第6段

Human behaviour, however, is having a detrimental impact on animal migration. The pronghorn, which resembles an antelope, though they are unrelated, is the fastest land mammal of the New World. One population, which spends the summer in the mountainous Grand Teton National Park of the western USA, follows a narrow route from its summer range in the mountains, across a river, and down onto the plains. Here they wait out the frozen months, feeding mainly on sagebrush blown clear of snow. These pronghorn are notable for the invariance of their migration route and the severity of its constriction at three bottlenecks. If they can’t pass through each of the three during their spring migration, they can’t reach their bounty of summer grazing; if they can’t pass through again in autumn, escaping south onto those windblown plains, they are likely to die trying to overwinter in the deep snow. Pronghorn, dependent on distance vision and speed to keep safe from predators, traverse high, open shoulders of land, where they can see and run. At one of the bottlenecks, forested hills rise to form a V, leaving a corridor of open ground only about 150 metres wide, filled with private homes. Increasing development is leading toward a crisis for the pronghorn, threatening to choke off their passageway.

然而，人类行为对动物迁徙产生了不利影响角马是新世界最快的陆地哺乳动物之一，尽管它们无关紧要。其中一群角马在美国西部大提顿国家公园的山区度夏，从山区的夏季范围沿一条狭窄的路线，穿过一条河流，到达平原地区。在这里，它们等待着冰封的几个月，主要以被风吹净雪的荒漠灌木为食。这些角马以它们迁徙路线的不变性和在三个瓶颈处的严重约束而著称。如果它们在春季迁徙期间无法通过个瓶颈，它们就无法到达夏季的牧场；如果它们在秋季无法再次通过瓶颈，逃往南部的那些被风吹的平原，那么它们很可能会试图在厚厚的积雪中冬而死亡。依赖远视和速度来躲避捕食者的角马，穿越高高的、开阔的陆地肩膀，这样它们才能看得见并奔跑。在其中一个瓶颈处，丛林覆盖的山丘升起形成一条V形，留下大约150米宽的一条开阔地带，上面布满了私人住宅。不断增长的开发正导致角马面临危机，威胁到它们的通道。

第7段

Conservation scientists, along with some biologists and land managers within the USA’s National Park Service and other agencies, are now working to preserve migrational behaviours, not just species and habitats. A National Forest has recognised the path of the pronghorn, much of which passes across its land, as a protected migration corridor. But neither the Forest Service nor the Park Service can control what happens on private land at a bottleneck. And with certain other migrating species, the challenge is complicated further – by vastly greater distances traversed, more jurisdictions, more borders, more dangers along the way. We will require wisdom and resoluteness to ensure that migrating species can continue their journeying a while longer.