Animal migration, however it is defined, is far more than just the movement of animals. 动物的迁徙，不管定义怎样，都远不止是动物们的移动。 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. 可以比较宽泛的描述成是发生在固定周期的包含某一个物种很多成员集体旅行，这个周期通常是一年一次，而且在很长时间的旅程之后才会有回报。 It suggests inherited instinct. 它让人想到了遗传下来的天性。 The biologist Hugh Dingle has identified five characteristics that apply, in varying degrees and combinations, to all migrations. 生物学家休丁格儿确认了五大特征，从不同角度，不同形式上来看，适用于所有迁徙。 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. 迁徙是带动物离开它们熟悉的栖息地，行程会比较长；迁徙的线路是直线形的，不是之字形的；在迁徙启程前和抵达时都会有特殊的行为，例如启程前要吃过量的食物；迁徙还需要特别的能量分配。 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. 还有一点就是：迁徙中的动物对这个伟大的行动会保有强烈的关注度，这会让它们不被诱惑干扰，也不会因一些让其它动物回避的挑战而止步。

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. 一种北极燕鸥，在它们从南美到极地圈的两万公里飞行中，都不会注意到沿途一些观鸟船上所散发的美味鲱鱼的味道。 While local gulls will dive voraciously for such handouts, the tern flies on. 但是，本地鸥却会贪婪地冲向这些施舍，那些燕鸥却会继续飞行。 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. 为什么？因为它们在飞行的当下，会被一种让我们人类都钦佩的某种本能所驱使：即远大的目标，所以，燕鸥们可以抵抗干扰。 In other words, it is determined to reach its destination. 换言之，就是抵达目的地的坚定决心。 The bird senses that it can eat, rest and mate later. 这些鸟类能意识到，它们以后有时间进食，休息还可以交配。 Right now it is totally focused on the journey; its undivided intent is arrival. 迁徙的当下，它们就会专注于行程；它们一心一意的目的就是抵达目的地。 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. 抵达北极某处其它极地燕鸥聚集的碎石海岸线对它们来说是在进化中形成的更远大的目的：找一个合适的地方，适当的时间，还有一个完善的环境，这样它们就可以成功地孵化，养育后代了。

But migration is a complex issue, and biologists define it differently, depending in part on what sorts of animals they study. 但是迁徙是一个复杂的问题，生物学家们对它的定义也是不同的，这部分取决于他们研究的动物种类。 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'. 美国蒙大纳大学的乔尔·伯杰，致力于研究美洲叉角羚和其它大型的陆地哺乳动物，喜欢他自己命名的简单、实际并适合于他研究的野兽的定义：从一个季节性的家园迁移到另一个家园然后返回。 Generally the reason for such seasonal back-and-forth movement is to seek resources that aren't available within a single area year-round. 一般来说，这样季节性的往返迁移的原因是为了寻找不能全年都在某一个地区找到的食物资源。

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. 但是，海洋里的浮游生物每天的垂直移动——夜里游上来觅食，白天沉下去躲避捕食者——也可视作迁徙。 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. 那么，同样的，蚜虫的这种运动也算是迁徙，当它们吃完了一株可食植物的嫩叶后，它们的幼仔就必须继续飞到另外一株寄主植物，且没有一只蚜虫会回到它出生的地方。

Dingle is an evolutionary biologist who studies insects. 丁格尔是一个进化生物学家，他研究昆虫。 His definition is more intricate than Berger's, citing those five features that distinguish migration from other forms of movement. 他的定义比伯杰的要复杂些，他引用了把迁徙和其他运动形式区分开来的五大特征。 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. 例如，他们考虑到一些事实，当蚜虫启程时，它们对（来自天空中的）蓝光会很敏感，当它们找到合适的着陆点的时候，会对（从嫩叶上反射的）黄光很敏感。 Birds will fatten themselves with heavy feeding in advance of a long migrational flight. 在长途迁徙飞行开始前，鸟儿们会吃大量的食物增肥。 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. 丁格尔认为，这种定义的价值在于，它把重点放在了角马和蚜虫的迁徙的共有现象，因此有助于研究人员理解进化是如何制造了所有的一切。

Human behaviour, however, is having a detrimental impact on animal migration. 但是人类的行为对动物的迁徙有着不利的影响。 The pronghorn, which resembles an antelope, though they are unrelated, is the fastest land mammal of the New World. 尽管两种动物没有关系，但是叉角羚看起来像羚羊，叉角羚是新大陆上最快的陆地哺乳动物。 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. 其中一个种群，在美国西部的大蒂顿山国家公园山区度过夏天，它们沿着夏季活动区的群山里的一条狭长路线出发，穿过河流，一直下到平原。 Here they wait out the frozen months, feeding mainly on sagebrush blown clear of snow. 在这里它们主要依靠风吹掉雪花后露出的灌木蒿为食，静待冰冻季节的结束。 These pronghorn are notable for the invariance of their migration route and the severity of its constriction at three bottlenecks. 这些叉角羚因它们恒定迁徙路线及在三个瓶颈处极为狭窄局促（的时间限定）而引人关注。 If they can't pass through each of the three during their spring migration, they can't reach their bounty of summer grazing; 如果春天它们不能在迁徙中通过这三个地方，它们就不能获得它们夏天谋食的回报。 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. 如果秋天，它们不能再次穿越这三个地方，逃离到这些常年大风的平原上，它们就有可能在试图熬过冬天的时候，丧命于深雪中。 Pronghorn, dependent on distance vision and speed to keep safe from predators, traverse high, open shoulders of land, where they can see and run. 叉角羚依赖于远距视觉和速度免受捕食者追捕，穿过高耸而开阔的地区，这里它们能够看得清，跑得快。 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. 在其中的一个瓶颈处，森林覆盖的山陡峭成V字形，只留下了开阔地区仅仅150米宽的一条走廊，这里满是私人房屋。 Increasing development is leading toward a crisis for the pronghorn, threatening to choke off their passageway. 越来越多的开发导致叉角羚的危机出现，它们的迁徙通道面临被切断的威胁。

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. 负责保护的科学家，一些生物学家，土地管理者们，美国国家公园管理局和其他一些机构现在不仅仅是致力于保护动物种和栖息地，也在维持动物的迁徙习性。 A National Forest has recognised the path of the pronghorn, much of which passes across its land, as a protected migration corridor. 叉角羚的迁徙路径大都通过国家森林的土地，这个地方已经被认定为一个受保护的迁徙走廊。 But neither the Forest Service nor the Park Service can control what happens on private land at a bottleneck. 但是，不管是森林管理局，还是公园管理局都无法控制在瓶颈处私人土地上发生的事。 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. 而且对于其它某些迁徙物种来说，这种挑战更加复杂，因为一路上要穿越更长到距离，更多的行政区和边界，沿途有更多的危险。 We will require wisdom and resoluteness to ensure that migrating species can continue their journeying a while longer. 我们需要智慧和坚定的信念去确保这些迁徙的物种能够更长时间地继续它们的旅程。