ff14欧米茄零式:[国家地理]探秘：动物迁徙之谜

Animal migration is a phenomenon far grander and more patterned than animal movement. It represents collective travel with long-deferred rewards. It suggests premeditation and epic willfulness, codified as inherited instinct. A biologist named Hugh Dingle, striving to understand the essence, 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 behaviors of preparation (such as overfeeding) and arrival; they demand special allocations of energy. And one more: Migrating animals maintain a fervid attentiveness to the greater mission, which keeps them undistracted by temptations and undeterred by challenges that would turn other animals aside.

动物迁徙是一种比动物活动更壮观、更模式化的现象。它表现为集体旅行，拥有长期递延的回报。它使人想到形成遗传本能的预谋和史诗般的固执。生物学家休·丁格尔识别出符合不同程度和组合的所有迁徙的五种特征，力争了解其本质。它们是带领动物离开熟悉的栖息地，持续时间很长的运动；它们的路线往往是直线而非锯形；它们包括特殊准备（如过量进食）和到达的习性；它们需要特别的能量分配。还有一点：迁徙动物热切关注更大的使命，因而不为诱惑所动，不受吓退其它动物的挑战所阻。

An arctic tern on its way from Tierra del Fuego to Alaska, for instance, will ignore a nice smelly herring offered from a bird-watcher's boat in Monterey Bay. Local gulls will dive voraciously for such handouts, while the tern flies on. Why? "Animal migrants do not respond to sensory inputs from resources that would readily elicit responses in other circumstances," is the dry, careful way Dingle describes it. In plainer words: These critters are hell-for-leather, flat-out just gonna get there. Another way, less scientific, would be to say that the arctic tern resists distraction because it is driven at that moment by an instinctive sense of something we humans find admirable: larger purpose.

举例来说，从火地岛前往阿拉斯加的北极燕鸥会无视蒙特利湾观鸟船送出的美味鲱鱼。本地鸥会贪婪地冲向这些施舍，而北极燕鸥却会继续往前飞。为什么？丁格尔以直白而谨慎的方式形容道，“在其它情况下，动物很容易对食物资源产生感知反应，但是迁徙动物对此没有反应。”简单地说：这些生物不顾一切、全力以赴，就是为了实现目标。另一种不太科学的方式说，北极燕鸥抗拒注意力分散，因为在那一刻，它受到某种本能的使命感的驱使，那是令我们人类敬佩的东西：更大的目标。

The arctic tern senses that it can eat later. It can rest later. It can mate later. Right now its implacable focus is 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.

北极燕鸥感觉到以后还可以吃，还可以休息，还可以交配。此刻，它不可改变的重点是旅行，它不可分裂的意图是抵达目的地。只要能到达北极某个铺满碎石的海岸线，那个其它北极燕鸥聚集的地方，就能实现更大的目标，按照进化的设计：找到它能成功孵化并养育后代的一个地点、一段时间、一组环境。

But the process is complex as well as various, and different biologists define it differently, depending in part on what sorts of animals they study. Joel Berger, of the Wildlife Conservation Society and 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. 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.

但是这个过程复杂多样，不同的生物学家为它下的定义也不同，这部分取决于他们研究的动物种类。野生动物保护协会及蒙大纳大学的乔尔·伯杰致力于美洲叉角羚及其它大型陆地哺乳动物的研究，更喜欢他所谓简单而实用的定义，很适合他研究的动物：“依照季节离开家乡，前往另一个家园，再返回。”一般来说 ，这种季节性来回迁徙的原因是为了寻找不能全年在某一个地区找到的食物资源。此外，海洋中浮游动物每天的垂直运动——夜里游上来觅食，白天沉下去躲避捕食者——也可以被视为迁徙。当蚜虫吃尽一棵食用植物上的嫩叶后，其后代就飞往另一棵寄主植物，没有一只蚜虫返回出生的地方。蚜虫的这种运动也可以被视为迁徙。

Dingle, an evolutionary biologist who studies insects, offers a more intricate definition than Berger's, citing those five features (persistence, linearity, undistractibility, special start-and-stop behaviors, stored energy) that distinguish migration from other forms of movement. 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 phenomena of the wildebeests and the sandhill cranes share with the phenomenon of the aphids and therefore helps guide researchers toward understanding how evolution by natural selection has produced them all.

研究昆虫的进化生物学家丁格尔下的定义比伯杰下的定义更复杂，他引用那五个特征（持久性、直线性、专注性、特殊的起止习性和能量储存）区分了迁徙和其它形式的运动。例如，在动身走上重要征程时，蚜虫会变得对（来自天空的）蓝光敏感，当它找到合适的着陆地点时，会对（脆弱的嫩叶反射出的）黄光敏感。在长途迁徙飞行开始前，鸟儿会吃大量的食物增肥。丁格尔认为其定义的价值在于，它把注意力集中在角马和沙丘鹤与蚜虫共有的现象，因此有助于引导研究人员理解依赖自然选择的进化如何制造了所有一切。

Rattlesnake migration on the Great Plains of western Canada is a peculiar but illuminating case. A young Canadian biologist named Dennis Jrgensen, now employed by the World Wildlife Fund, studied movements of the prairie rattlesnake (Crotalus viridis viridis) on the outskirts of Medicine Hat, Alberta, near the northern limit of its range, and found the snakes migrating ambitiously each spring and fall. The average round-trip by his animals was about 5 miles, though an earlier study detected Canadian rattlesnakes migrating as far as 33 miles. In Arizona, by contrast, rattlers don't travel nearly so far, because they don't have to. The driving logic of the Canadian migrations is related to cold winter temperatures (always difficult for reptiles) and the scarcity of really good den sites in which to survive hibernation.

加拿大西部大平原的响尾蛇迁徙是奇特而具有启发性的个例。现受雇于世界野生动物基金会的加拿大年轻生物学家丹尼斯·乔根森，在亚伯达梅学哈特郊区北部边界附近研究大草原响尾蛇的活动。他发现这些蛇每年春秋都雄心勃勃地进行迁徙。这些动物平均往返约5英里（约8公里），但是早期的研究发现加拿大响尾蛇迁徙的距离达33英里（约53公里）。与之相反，美国亚利桑那州的响尾蛇几乎至今都不旅行，因为它们不需要旅行。驱使加拿大响尾蛇迁徙的必然原因与寒冷冬季的气温（爬行动物难以忍受）有关，也与缺乏安然冬眠的真正优良的巢穴地点有关。

"There aren't many dens that can support survival over winter on this landscape," Jrgensen told me. An ideal den must be deep underground, where the earth is warm, but accessible from the surface via burrows or natural fissures. Such refuges are few and far between. "Because of that, what you get is very large aggregations of snakes at these communal dens." Picture a serpentine tangle of a thousand snakes, piled together cozily, calm and sleek in their subterranean nook, jointly awaiting the signals of spring. When surface temperatures rise to a comfortable threshold, they emerge. For a while they bask in the sunlight, crowded like bronzed tourists on the Costa del Sol. But the rattlesnakes are hungry. What's their next imperative? To get away from one another, find food, and mate. So they migrate radially—in all possible directions away from the den—like starburst embers from a Fourth of July rocket.

乔根森告诉我，“这个地区有许多可供过冬的巢穴。”理想的巢穴必须深入土壤很温暖的地下，但可以通过地洞或自然裂缝从地面进入。这样的避难所寥寥可数。“因此，在这些公共巢穴中，你会发现非常庞大的蛇群。”想像一下，上千条盘绕纠结的蛇安逸地堆叠在一起，在它们那秘密的隐匿处平静地滑动，共同等待着春天的信号。当地面温度升到舒适的临界点时，它们就涌出来，像在太阳海岸晒成古铜色的游客一样挤在一起，在阳光下晒一会。但是，这些响尾蛇饿了。它们必需做的下一件事是什么呢？彼此分开，寻找食物，进行交配。于是，它们呈放射状移动——从巢穴向所有可能的方向迁移——像国庆焰火似的四射开来。

Jrgensen used small radio transmitters, surgically implanted, to chart this pattern, tracking the individual routes of 28 different rattlesnakes during 2004 and 2005. More recently, on a blazing summer day, he took me back to one of the den sites, in a slumping bank above the South Saskatchewan River. The slumping had opened deep underground cracks in which roughly 60 prairie rattlers had wintered. From the riverbank we turned toward the uplands and began retracing the migration route of one of his animals, an ambitious female he had labeled E.

在2004年和2005年期间，乔根森利用手术植入的小无线电发射机跟踪28条不同响尾蛇的单独路线，绘制出这种模式图。最近，在夏天一个炽热的日子，他带我回到南萨斯喀彻温河坍塌河岸上这样一个巢穴地点。坍塌的河岸打开了深入地下的裂缝，大概有60条大草原响尾蛇在那里过了冬。我们从河岸转向高地，开始回溯一条蛇——一条雄心勃勃的雌性蛇，他标记为E——的迁徙路线。

Not far upslope were three rounded boulders, lichen-covered, with a hole beneath. Snake E had arrived here on May 8, Jrgensen said; she rested, basked, and took off again on May 27. She ascended this steep bench (we started climbing) amid the sage and crumbling gray mud, then slithered back down the slope (we plunged after her), crossed this dirt road, crossed this moist gulch full of goldenrod and skunkbrush (we thrashed through), and climbed again. Back atop the bench, we ducked between strands of barbed wire into the corner of a crop field irrigated by center pivot. The crop had been alfalfa when E came through; this year, potatoes. We politely circumvented the spud field and picked up her track on the far side, between several more center-pivot circles, blooming bright yellow and rank with canola. The midday air, hot and thick, smelled like baked fish from an oven.

坡上不远处有三个覆盖着青苔的圆石，下面有一个洞。乔根森说，E在5月8日来到这里，休息、晒太阳，然后在5月27日又出发了。她爬上鼠尾草和破碎灰泥之间这块陡峭的岩架（我们开始爬），然后滑下斜坡（我们随她跳下），通过这条泥路，越过长满金麒麟草和臭灌木的潮湿峡谷（我们劈开荆棘穿过去），再继续爬。回到岩架顶上，我们躲开带刺的铁丝网进入由中心旋转系统灌溉的农田拐角。E通过时，这里种的是苜蓿，今年，这里种的是土豆。我们斯文地绕过土豆地，在远侧几个中心旋转系统圈之间找到它的踪迹，那里盛开着繁茂的亮黄色油菜花。正午的空气炎热而混浊，散发出火炉烤鱼的味道。

Having sprinted across two pivot fields in a single day, brave lady, E had then picked up the security of a fence line, where the weeds were dense and the discs of a tiller, the blades of a swather, never touched. By late June she was making 200 yards daily, still along the fence line, amid a hospitable jumble of rocks, weeds, and rodent burrows. At that point Jrgensen and I paused in the shade of a cottonwood to rest. We had covered eight weeks of rattlesnake migration in four hours and were drenched with sweat.

在一天之内全速通过两块有中心旋转系统的田地之后，勇敢的E女士选择了安全警戒线，那里野草密集而且农具的圆盘——割谷机的刀片永远也碰不到它。6月末，她每天滑动200码（约183米），仍然沿着这条警戒线，在混杂着岩石、野草和鼠洞的友好环境中游动。我和乔根森在那个地方停下来，在杨树的荫凉处休息。四个小时之内，我们走过了响尾蛇八个星期经过的迁徙路程，已经汗流浃背了。

Hereabouts was where E had spent most of her summer that year, mating at least once and fattening herself on rodents for the homeward migration, another winter in the den, and pregnancy. It was productive habitat but also risky, Jrgensen said, what with all the agricultural machinery that could dice a snake like zucchini, all the farm-road traffic that could flatten her like an alligator belt. The changes that had come to this landscape did not favor long-distance rattlesnake migration. At that moment, as though to embody those changes within one human memory, a man named Aldo Pederzolli pulled up on his four-wheeler.

E在这一带度过了大部分夏季时光，至少交配过一次，还吃老鼠增肥，为迁移回家在巢空中过冬怀孕作准备。乔根森说，这是肥沃的栖息地，也充满了危险，因为这里所有的农业机械都能像切南瓜一样切碎响尾蛇，所有的农场道路运输都能把它压得像鳄鱼皮带。这块地发生的变化不利于响尾蛇长距离的迁徙。正在这时，好像要在人类记忆中体现这些变化似的，一位名叫奥尔多·派德左利的男子停下了他的四轮车。

Pederzolli was the farmer on whose land we stood and who had genially welcomed Jrgensen's study. He wore a black polo shirt, rubber boots, and a cap that read "Cee-Gee Earthmoving." He was a fit-looking man of 80, with squinty brown eyes, a high voice, a sun-ripened Canadian smile. Introduced to me, hearing the reason for my visit, he said, "Oh, I just love rattlers." This wasn't irony. Got enough good snakes, he added, and you don't need to worry about gophers. Back when he was young, Pederzolli recalled, he would see nice fat old rattlers, that big around, when he seeded a fallow field. Don't see such big ones anymore. There was a den near the river, he said wistfully, and they'd migrate six miles up to a nice patch of open prairie full of gophers. Not anymore.

派德左利是我们站着的这块地的主人，他高兴地支持乔根森的研究。他身穿黑色球衣，橡胶靴子，戴着印有“Cee-Gee Earthmoving”字样的帽子。他是位80岁的老人，看上去很健康，有双斜视的棕色眼睛，高嗓门，面带加拿大人阳光成熟的微笑。他向我做了介绍，得知我来访的原因后说，“噢，我只是喜欢响尾蛇。”这不是反话。他接着说，只要有足够的好蛇，就不必担心有地鼠了。派德左利回忆说，年轻时，自己在播种休耕田的时候，会看到又胖又老的响尾蛇，那么引人注目。现在再也看不到那么大的蛇了。他留恋地说，河边有一个巢穴，它们向上迁移了6英里（约9.66公里），到开阔草原地鼠多的好地块去了。现在不一样了。

Although it's only a hypothesis, Dennis Jrgensen suspects that natural selection—in this case, the death of the venturesome—may be turning his migrating rattlesnakes into a population of stay-at-homes.

虽然只是假设，但是丹尼斯·乔根森怀疑，也许是自然的选择——在此例中就是死亡的危险——正在将他的迁徙响尾蛇转变为居家种群。

Biological diversity entails more than a gross tally of species. Diversity of ecosystems, behaviors, and processes are important too, contributing richness and beauty, robustness and flexibility and interconnectedness to the living communities on Earth. To lose the long-distance migrations performed by some species would be a grievous diminution. Joel Berger has made this point in the journal Conservation Biology and elsewhere, with reference to migrating species around the world and one creature close to home: the pronghorn (Antilocapra americana), North America's only endemic species of ungulate.

生物的多样性需要更多物种的聚合生存。生态系统的多样性、习性和发展过程也很重要，它为地球上的生活社区提供了丰富而美丽的东西，促成了其稳健性、灵活性和互联性。失去由某些物种执行的长距离迁徙活动将是令人痛心的衰退。乔尔·伯杰根据世界各地的迁徙物种和一种离家不远的生物：北美洲特有的有蹄物种叉角羚，在《保护生物学》及其它杂志上证明了这一点。

Loose talk sometimes mistakes the pronghorn for an antelope, but in fact it belongs to a family all its own. Its extreme speed (fastest land mammal of the New World), more than necessary to evade any living North American predator, probably reflects adaptation for escaping the now extinct American cheetah of the Pleistocene. Besides traveling fast, though, the pronghorn also travels far. One population migrates hundreds of miles across the Great Plains from north-central Montana into southern Saskatchewan and Alberta. Another population follows a narrow, tenuous route from its summer range in Grand Teton National Park, across a divide at the headwaters of the Gros Ventre River, and down onto the plains south of Pinedale, Wyoming, in the Green River Basin. There the pronghorn mingle with thousands of others arrived from other parts of Wyoming, where they try to distance themselves from the natural gas wellheads and drilling teams, and wait out the frozen months, feeding mainly on sagebrush blown clear of snow.

闲谈中，人们有时会把叉角羚说成羚羊，其实它属于完全独立的家族。它的速度极快，超过了逃避北美所有现存捕食者所需要的速度，是美洲新大陆最快的陆地哺乳动物。也许这反映了它的适应性，避免了重蹈现已灭绝的更新世美洲猎豹的覆辙。叉角羚不仅跑得快，而且跑得远。一个种群从蒙大纳中北部越过大平原，历经上千公里进入南萨斯喀彻温和亚伯达。另一个种群从大提顿国家公园的夏季活动区出发，沿着一条狭窄的路线在格罗文特河源头跨越分水岭，进入绿河流域怀俄明州的派恩代尔南部平原。在那里它们与成千上万来自怀俄明其它地区的叉角羚会合，设法避开天然气井和钻井队，只吃吹掉雪花露出的蒿子，等待寒冷季节的结束。

The Grand Teton pronghorn are notable for the invariance of their migration path and the severity of its constriction at three critical spots, known as Trappers Point, the Red Hills, and the Funnel. Field research by Berger and colleagues has charted that path and illuminated its jeopardies. If the pronghorn can't pass through each of the three bottlenecks during their spring migration, they can't reach their bounty of summer grazing in Grand Teton National Park; if they can't pass through again in autumn, escaping south onto those windblown plains, they'll likely die trying to overwinter in the Jackson Hole area or get fatally stuck in the deep snows of the divide. On a bright day in November, in company with a biologist named Renee Seidler, I went for a look at the details of their dilemma.

大提顿公园的叉角羚更值得注意，是因为它们的迁徙路线一成不变，并受到三个关键地点（“捕捉器地点”、“红山”和“漏斗”）的严重威胁。伯杰及其同事进行实地考察，绘制出这条路线，并说明了它们的危险处境。在春季迁徙的过程中，如果叉角羚通不过这三个瓶颈，就无法获取在大提顿国家公园享受夏季的奖赏。如果秋季它们无法再通过三个瓶颈，逃离南方，进入那些微风吹拂的平原，就很可能在试图在杰克逊洞区过冬时死去或在分水岭陷入深雪而丧命。11月一个明媚的日子，我和生物学家蕾妮·塞德勒结伴前去详细查看它们的窘境。

Seidler, also employed by the Wildlife Conservation Society, works mostly on habitat issues in the booming gas fields between Pinedale and Rock Springs, an area that supports perhaps 20,000 pronghorn each winter. The northward migrants constitute just a fraction of that total but are special, she noted, because without them, one of America's great western parks, Grand Teton, would entirely lack one of America's great western species. On a knoll at Trappers Point, we read the historical marker about fur trappers and Nez Perce and Crow peoples gathering here to trade and gazed down at the modern manifestations of growth and commerce alongside Highway 191: a sprawling little community known as Cora Junction. There were about 50 houses, trailers, and other buildings, including a Jehovah's Witnesses meeting hall, all nested within a grid of streets and lanes, fenced yards, dogs, chickens, real estate signs, old tires, boats on trailers, a weathered trampoline, and a rusting green Chrysler from the 1940s. Right about here, Seidler said, pointing to a gap of sage between our knoll and the houses, is where most of the pronghorn seem to cross through.

塞德勒也受雇于野生动物保护协会，她主要研究派恩代尔和罗克斯普林斯之间蓬勃发展的天然气田中的栖息地问题。这些地区每年冬天都要供养约两万头叉角羚。她强调说，向北迁移只构成其全部迁徙的一小部分，但是很特别。因为没有它们，美洲西部大公园之一大提顿将完全失去一种美洲西部的大物种。在“捕捉器点”的一个小山上，我们看了历史纪念碑，上面记录的是皮毛猎人和内兹佩尔塞及克罗人聚集在这里交易的事情。我们凝视着191号高速公路沿线发展和贸易的现代化表现：被称为“科拉枢纽”的无规划开发的小社区。那里有约50幢房屋、拖车式房屋和其它建筑，其中包括耶和华见证会的会议厅，一切都处于由街道和巷子组成的网格里。那里有围了栅栏的庭院，狗、鸡、房地产标志、旧轮胎、在拖车上的小船，一个风华了的弹簧垫以及一辆1940年代的锈渍斑斑的绿色克莱斯勒车。塞德勒指着我们所在小山和房屋间的鼠尾草豁口说，看起来大多数叉角羚就从这里通过。

We drove north on a county road about 20 miles, along willowy bottomlands of the upper Green River, tracing the migration route. Pronghorn, dependent on distance vision and speed to keep safe from predators, do not like willowy bottomlands, Seidler explained. They don't like dense forest either, so they traverse these high, open shoulders between the river and the woods, where they can see and run. Then we came to a place where forested hills rose on both sides of the river to form a soft V, leaving a corridor of open ground only about 150 yards wide. "That's the Funnel," Seidler said. It was private land, dissected by the driveways, the buck-and-rail fences, the arched gateways of people wealthy enough to have a second home, or a third, on the headwaters of the Green. On this day, in the off-season, there was no sign of anyone around.

我们在乡村公路上向北行驶了20英里（约32公里），沿着上绿河柳树成荫的洼地跟踪叉角羚的迁徙路线。塞德勒解释说，叉角羚依赖远距视力和躲避捕食者的速度，不喜欢柳树成荫的洼地。它们也不喜欢密集的树林，因此它们穿过河流和树林间这些高耸而开阔的山肩，在这里它们能够看得见，跑得快。接着，我们来到一个地方。这里的河流两边高耸起树木丛生的小山，形成坡度缓和的V字形，留下只有约150码（约137米）宽的开阔走廊。“这是‘漏斗’。”塞德勒说。这是位于绿河源头的私人土地。那些有能力拥有第二或第三个家的有钱人用车道、架子横杆围栏，和拱形通道将这里划分成几部分。这一天是淡季，周围没有人迹。

One more yard fence, one more house, one or two large barking dogs, could make a bad difference. As at Trappers Point so here at the Funnel; incremental human activities are accumulating toward a crisis for Grand Teton's pronghorn—threatening to choke off their passageway.

多一处庭院篱笆，多一幢房屋，多一两条狂吠的大狗，都可能形成不利的变化。“漏斗”这里像在“捕捉器点”一样，人类活动的增加正在积累大提顿叉角羚的危机——将要切断它们的通道。

Conservation scientists such as Berger, along with some biologists and land managers within the National Park Service and other agencies, are now working to preserve migrational behaviors, not just species and habitats. The Bridger-Teton National Forest has recognized the path of the Grand Teton pronghorn, much of which passes across national forest land, as the first federally protected migration corridor. But neither the Forest Service nor the Park Service can control what happens on private land at a bottleneck, nor on Bureau of Land Management parcels within the drilling fields south of Pinedale. 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.

伯杰这样的保护科学家以及美国国家公园管理局和其它机构的一些生物学家和美国土地管理者不仅在保护物种和栖息地，也在努力维持动物的迁徙习性。大提顿国家公园叉角羚的迁徙路径大都通过国家森林的土地，布里杰-提顿国家森林已经把那里确定为第一个受联邦保护的迁徙走廊。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领地上发生的事，也无法控制在派恩代尔南部土地管理局地块上的钻井地点发生的事。对于其它某些迁徙物种来说，这种挑战更加复杂——因为一路上它们要穿越更长的距离、更多的行政区、更多的边界，经历更多的危险。

Imagine, for instance, that you're a lesser sandhill crane (Grus canadensis canadensis), setting off on your spring migration from southwestern Texas. You might have to fly across a corner of New Mexico and Oklahoma, then Kansas, Nebraska, South Dakota, North Dakota (most of which allow hunting of sandhills), then over the Canadian border into Saskatchewan, angling northwest across Alberta and British Columbia, across Yukon Territory, then the breadth of Alaska, and finally across the Bering Strait to your summer breeding grounds in northeastern Russia. This would be a trip of roughly 5,000 miles. Needing to pause somewhere and replenish yourself, you would probably stop on the Platte River in Nebraska, near the town of Kearney. If so, you’d have company. About 500,000 northbound sandhills make the same stopover every year.

举例来说，设想你是一只较小的沙丘鹤，从德克萨斯西南部出发，开始春季迁徙。也许，你必须飞过新墨西哥州和俄克拉荷马州一角，然后经堪萨斯州、内布拉斯加州、南达科塔州、北达科塔州（这些地区大都允许捕猎沙丘鹤），再越过加拿大边境，进入萨斯喀彻温，转向西北越过亚伯达和不列颠哥伦比亚、跨过育空地区，再飞越阿拉斯加，最后横渡白令海峡，抵达俄罗斯东北部你的夏季繁殖地。这将是约5,000英里（约8046公里）的旅程，你需要在某处逗留，为自己补充食物，也许你会在科尔尼镇附近内布拉斯加州境内的普拉特河停下来。这样的话，你会遇到伙伴，因为每年大约有500,000只往北飞的沙丘鹤中途会在同一地点停留。

There they linger for two or three weeks, maybe four. Some depart onward as others arrive, keeping the average crane count during March and April at around 300,000. By night they roost in the gently flowing shallows of the Platte, shin-deep in cool water, or else on sandbars, giving them warning against any predator that might come splashing out. Each morning they rise up in vast, graceful waves and fly to fields nearby, where they spend their days assiduously feeding on waste corn the harvesters missed and earthworms and other invertebrates. Such a stopover period is no exception to the undistractibility of migrating animals, as defined by Hugh Dingle; it's a part of the whole program, repeated by generations of cranes. During this stopover, a six-pound lesser sandhill adds about a pound and a half of fat to its weight. (The greater sandhill, another subspecies also present on the Platte, is larger.) The birds need that fat between Nebraska and Russia. Therefore, they need the stopover habitat—the shallows, the sandbars, the security, the corn and invertebrates—to complete their arduous yearly cycle.

它们在那里消磨两、三个星期，或四个星期。在三、四月份，有其它鹤到达时，就会有一些向前飞，使这里鹤的平均数保持在约300,000只。在夜里，它们栖息在普拉特河缓缓流动的浅水处，呆在没腿的凉爽河水中或沙洲上，因为溅起的水花会警告它们，可能有捕食者来了。每天早上，它们从广阔优美的波浪中起飞，飞到附近的田野，全力以赴地吃着收获者遗留下来的玉米和蚯蚓及其它无脊椎动物。正如休·丁格尔所下的定义，专注的迁徙动物毫不例外地都要经历这样的中途停留期。这是整个计划的一部分，为一代代沙丘鹤重复着。在中途停留期间，体重不到六磅（约2.72公斤）的沙丘鹤会增加约一磅半（约0.68公斤）的脂肪。（较大沙丘鹤——也出现在普拉特河的另一亚种——增重更多。）在内布拉斯加州和俄罗斯之间飞行时，那些鸟需要那些脂肪。因此，它们需要这个中途停留的栖息地——浅滩、沙洲、安全、玉米和无脊椎动物——来完成年复一年的努力。

I stood overlooking that habitat, on a morning in late March, and watched wave after wave of cranes rise from the river. Each group climbed clumsily off the water, gained elegance as their wings caught more air, turned in formation, and flew out to their daily feeding. Meanwhile, they called to one another in their distinctive, creaky trill. There were maybe 60,000 sandhills just within the sweep of my binoculars. It was a spectacle of extraordinary abundance, a reminder of what America looked like back when John James Audubon stared up at sky-clogging flocks of passenger pigeons, when George Catlin saw the thunderous migrations of bison.

三月末的一天早晨，我站着俯瞰那处栖息地，看着一波又一波沙丘鹤从河里起飞。一群群鹤笨拙地飞离水面，当它们的翅膀捕捉到更多空气时，就优雅地形成编队，飞往每天的捕食地。与此同时，它们用叽叽嘎嘎与众不同的颤音彼此呼唤。仅在我的双筒望远镜视野之内，就有大概60,000只沙丘鹤。那是由惊人数量形成的奇观，不禁令人回想起美洲的过去——约翰·詹姆斯·奥杜邦仰望候鸟群遮天蔽日的景象，乔治·卡特林看到北美野牛轰隆隆迁徙的景象。

I had watched fly-in of the cranes too, on an earlier evening, when they arrived back through the twilight and settled onto their shoals for the night. But I found fly-out more deeply affecting—because, I suppose, the birds at daybreak are headed off with a purpose, not just home to rest. They would fatten themselves for another long leg of their journey. Their travel would take them to safe and bountiful breeding grounds. Their prodigious efforts, their resistance to distraction, would yield new cohorts of sandhill cranes, extending and rejuvenating the species. I almost wrote "perpetuating the species," but no, we can't be sure of that. Nothing alive is perpetual.

此前的一天傍晚，我还看到沙丘鹤飞来的情景：它们在暮色中归来，安顿在浅滩上过夜。可是，我发现，它们飞出去的景象更加动人。我想，那是因为黎明时的鸟儿怀着目的出发，而不只是回家休息。它们为走上另一个长期的旅程而使自己胖起来。它们的旅行会把它们带到安全而丰裕的繁殖地。它们的惊人努力，它们抗拒分心的努力将产生新的沙丘鹤军团，将发展更新这个物种的活力。我差点要写“永久保存这个物种”了，可是，不行，我无法肯定这一点，因为活着的一切都不可能永存。

It was the accrued wisdom and resoluteness of evolution that I was witnessing, airborne above the Platte. If we humans have accrued equal wisdom and can summon equal resoluteness, I thought, maybe we'll allow them to continue their journeying a while longer.

我亲眼目睹进化累积的智慧和信念在普拉特上空传播。我想，如果我们人类累积起同样的智慧，能够鼓起同样坚定的信念，也许我们能让它们更长时间地继续他们的旅程。

添加新评论

相关文章：

【产经抄】10月26日

【设计图集】精美的清真寺建筑

游走在帕米尔高原

地质奇观：埃兰弯的彩虹

【国家地理】2010年国家地理摄影大赛画廊(自然，第4周)