我们的星球（2019）

‎密苏里州的黄土断崖
Missouri's Loess Bluffs.
‎这是它们在漫长的北上旅途中
It's one of the most important stop-off points
‎最重要的停靠点之一
on their long journey north.
‎它们的停留时间取决于天气
How long they will stay depends on the weather.
‎在二月 从北极吹来的冰冷寒风
In February, icy winds blowing down from the Arctic
‎会导致气温突然下降
can cause temperatures to suddenly fall.
‎如果这里的温度都很低
And if it's freezing here
‎那么它们要去的地方 情况会更糟
conditions will be far worse where they're headed.
‎所以目前 ‎所有前往北方的航♥班♥都暂停了
So, for now, all flights north are suspended.
‎它们虽然是雪雁
They may be snow geese
‎但它们在冰面上待得并不舒适
but they don't seem to be at home on the ice.
‎随着湖泊边缘被冰冻
With the lake's margins frozen
‎鸟类都被集中到湖中心
the birds become concentrated in the center.
‎越是拥挤 越是没有回旋的余地
The busier it gets, the less room there is for maneuver.
‎这也适合另一位访客
And that suits another visitor.
‎白头海雕从北美各地
Bald eagles come here...
‎来到这里
...from across North America.
‎它们的到来时间 与雪雁的时间一致
And they time their arrival to coincide with that of the snow geese.
‎雪雁体型太大 无法在飞行中被捕获
The geese are far too big to be snatched on the wing
‎因此白头海雕采取了不同的捕猎策略
so the eagles use a different hunting strategy.
‎它们朝雁群飞去 将雪雁们吓到空中
Flying at the flock, they scare the birds into the air.
‎雁群越拥挤 对白头海雕来说就越好
The tighter the geese are packed, the better it is for the eagles.
‎雪雁在恐慌中彼此相撞
In their panic, geese collide with one another
‎撞坏翅膀脚爪
and limbs are broken.
‎受伤的雪雁被留在冰面上 孤立无援
Injured birds are left high and dry on the ice
‎或者无法从水下逃跑
or unable to escape underwater.
‎只要寒流持续 ‎它们就会持续如此脆弱
All will remain vulnerable for as long as this cold snap lasts
‎前行之路仍然受到冰雪的阻挡
their onward migration still blocked by ice and snow.
‎回到北极 太阳开始慢慢变强
Back in the Arctic, the sun is slowly beginning to strengthen.
‎但到二月下旬
But in late February
‎太阳光还只是勉强出现在地平线上
its rays still barely show above the horizon.
‎在这种严寒的环境下 食物极少
In such frigid conditions, there's little to eat
‎大多数动物向南撤退
and most animals retreat southwards
‎或者完全停止活动
or shut down altogether.
‎但这一只什么都没有做
But this one does neither.
‎一只猞猁 世界上生活在最北端的猫
A lynx, the most northerly cat in the world.
‎它能够很好地抵御寒冬 ‎所以它不用撤退
It's well protected from the cold, so it doesn't retreat.
‎但它可能得走很远才能找到食物
But it may have to travel huge distances to find food.
‎有一只猞猁被记录
One was even recorded
‎在短短一年间行进三千公里
walking more than 3,000 kilometers in just one year
‎超出所有人的想象
further than anyone thought possible.
‎（北太平洋）
‎这种猫几乎只依赖一种猎物
This cat relies almost entirely on just one kind of prey.
‎而现在 这种猎物数量极少
And right now, there are very few around.
‎北极兔
Snowshoe hares.
‎发现它们只是挑战的一半
Spotting one is only half the challenge.
‎猞猁几天就需要进食一次
Lynx need to eat every few days
‎所以它的搜寻永无止境
so his search never ends.
‎它很幸运
He's in luck.
‎它发现了另一种气味
He has detected another scent.
‎北极兔保持警觉
The hare holds its nerve
‎并相信自己的伪装
and trusts its camouflage.
‎猞猁的速度 ‎不可能长时间快于它的猎物
The lynx can't outpace his prey over a long run
‎所以它需要靠近
so he needs to get close.
‎终于吃上了一顿
A meal at last.
‎（三月）
‎随着地球的北半球向太阳倾斜
As the Earth's Northern Hemisphere tilts back towards the sun
‎带来了三月更长的白昼
bringing the longer days of March
‎叉角羚开始了一年一度的迁徙
pronghorn antelope start their annual migration.
‎这段旅程将把它们 ‎从怀俄明州南部白雪皑皑的平原
Their journey will take them from the snowy plains of southern Wyoming
‎带到落基山脉郁郁葱葱的山谷中
to the lush valleys of the Rocky Mountains
‎它们将在那里分娩
where they will give birth.
‎但是今天 ‎它们的路径已经发生巨大的变化
But today, their path has changed beyond recognition.
‎首先 它们必须找到 ‎一条穿过油田和气田的路
And to start with, they have to find a way through oil and gas fields.
‎一只雄性要碰碰运气
A male tries his luck.
‎叉角羚很谨慎
Pronghorn are cautious
‎尤其是遇到人类时
especially when encountering humans.
‎目前为止 一切顺利
So far, so good.
‎现在轮到其他叉角羚了
Now for the rest of the herd.
‎准备…走！
And... go!
‎在接下来的几个月里
Over the next couple of months
‎它们会行进200公里
they will travel 200 kilometers
‎以到达它们位于北方的繁殖地
to reach their calving grounds in the north.
‎这段旅程的挑战性逐年提升
A journey that gets more challenging every year.
‎为防止牲畜逃跑而设计的围栏
Fences that were designed to keep livestock in
‎防止叉角羚进入时同样有效
are equally effective at keeping pronghorn out.
‎但这是它们祖先走过的路线
But this is the route their ancestors took
‎所以它们坚持不懈
so they persevere.
‎最近 一只叉角羚 ‎在向北迁徙的过程中
Recently, one pronghorn crossed nearly 150 fences...
‎越过了近150道栅栏
...on its migration north.
‎但是叉角和带刺的铁丝
But pronged horns and barbed wire
‎可能并不相合
can be an unhappy combination.
‎栅栏远远不是唯一的问题
And fences are far from the only problem.
‎更危险的是那些横穿它们路线的公路
More perilous are the highways that now cut across their path.
‎它们可能是美洲最快的陆地动物…
They may be the fastest land animal in the Americas...
‎但它们经常无法躲避汽车
...but they can't always dodge a car.
‎过去200年带来的变化
The changes brought by the last 200 years
‎使叉角羚的数量减少了九♥成♥以上
have reduced pronghorn numbers by over 90%.
‎但还有一些好消息
But there is some good news.
‎叉角羚忠于祖先的路线
The pronghorn's loyalty to ancestral routes
‎使得人类有可能 ‎在关键的穿越节点上建造立交桥
has made it possible to build overpasses at key crossing points
‎这几乎消除了该地区的公路死亡
and that has almost eliminated road deaths in the area.
‎随着叉角羚群向北移♥动♥ ‎它们到达了真正的狂野西部
As the herd continues north, they reach the real wild west.
‎在这里它们必须面对的 ‎不是人造的障碍
Here, they must face not human-made obstacles
‎而是自然的障碍
but natural ones.
‎积雪正在融化
The snow is now melting
‎显示它们正在按计划前往繁殖地
showing that they're on schedule to reach their calving grounds
‎正好能赶上在那里分娩
just in time to give birth there.
‎但季节变化 也会带来问题
But the seasonal changes also bring problems.
‎前方是怀俄明州的格罗斯温特河 ‎现在已被融水填满
Ahead lies Wyoming's Gros Ventre River, now swollen with meltwater.
‎叉角羚必须穿过这条河 ‎才能到达繁殖地
The pronghorn must cross it to get to their breeding grounds
‎它们看起来很紧张
but they seem nervous.
‎不是害怕河流本身
Not about the river itself
‎而是可能潜伏在河对岸的捕食者
but what predators may be hiding on the opposite bank.
‎在水里
In the water
‎它们在陆地上的速度几乎没有意义
their speed over land will be of little relevance.
‎但狼和美洲狮等捕食者
But predators, such as wolves and cougars
‎现在已被猎杀得几乎绝迹
have now been hunted almost to extinction
‎所以在这里遇袭的机会很小
so the chances of an attack here are slim.
‎只是叉角羚并不知道这一点
It's just that the pronghorn don't know that.
‎谨慎行事还是值得的
It still pays to be cautious.
‎这让它们走到了今天
It's got them this far.
‎出发的几周后
Several weeks after setting off
‎它们终于到达了繁殖地
they, at last, reach their breeding grounds.
‎洛基山脉的肥沃山谷
The fertile valleys of the Rocky Mountains.
‎（北太平洋）
‎墨西哥的巴哈半岛
Mexico's Baja peninsula
‎并没有经历北方的寒冷冬季
doesn't experience the cold winters of the north.
‎因此每年的此时 温和的温度
So the mild temperatures of its seas at this time of the year
‎使其成为世界上最伟大的
make it an excellent seasonal retreat
‎一种长途旅行者 ‎最为青睐的季节性度假胜地
for one of the world's greatest long-distance travelers.
‎灰鲸
Gray whales.
‎现在是三月中旬
It's mid-March
‎六周前 这位雌性在这里分娩了
and six weeks ago, this female gave birth here.
‎隐蔽的水域很温暖 没有捕食者
The sheltered waters are warm and free from predators.
‎这里是很棒的育婴室
It's an excellent nursery.
‎但这种完美是有代价的
But such perfection comes at a cost.
‎这里没有这位母亲的食物 ‎而它从12月开始就待在这里了
There's no food for this mother, and she's been here since December.
‎因此 只要它的幼崽足够强壮
So as soon as her calf is strong enough
‎它就会带领幼崽往北走八千公里
she will lead him 8,000 kilometers north
‎前往阿♥拉♥斯加白令海的觅食地
to their feeding grounds in Alaska's Bering Sea.
‎这是所有哺乳动物中最长的迁徙