VOA标准英语2013--卫星帮助解释斑马的迁徙

 

Satellites Help Explain Zebra Migration¹ 卫星帮助解释斑马的迁徙

Every year, zebras in Botswana begin a 580-kilometer migration looking for food. Even though it’s an annual event, researchers only had a general idea when it would start and they didn’t know which route the animals would take or why. That is, until now.

Sometime in September, zebras begin their trek² from Botswana’s Okavango Delta³ to the Makgadikgadi Salt Pans. Pieter Beck, a research associate at the Woods Hole Research Center, was among those studying the migration.

“Like most large herbivores that naturally migrate, zebra migrations⁴ have been under threat. Across the globe, most of the big migrations already are under threat. So, conserving⁵ the ones that exist is of course important; and finding ways where people and wildlife can live together is critical if you want to achieve that,” he said.

One big mystery was how do zebras choose the route to the salt pans? It was not because the knowledge had been passed down from one generation to the next. Researchers knew that between 1968 and 2004 veterinary fences were built across potential migration routes. The fences were put up to help prevent wild buffalo⁶ from transmitting disease to cattle.

Within three years of the fences being taken down, the zebras began to migrate. Now, keep in mind that the fences were up for 36 years and that zebras usually live no more than 12 years in the wild.

“The fences were up longer than the lifespan of the zebra. So the zebra that we tracked making this hundreds of miles of migration – they couldn’t have learned it from their parents. So they actually rediscovered it using probably exploratory walks. It’s a very fascinating story in that sense and sort of a good news story in conservation. And these are unfortunately rare these days,” said Beck.

So, researchers turned to the U.S. space agency NASA and took a close look at some of its satellite images and data.

“The NASA instruments that we worked with orbit the Earth and they give us a global picture of rainfall and of vegetation productivity. So those are the two metrics we extracted. The rainfall data you can get for the tropics in particular. And we can see every six hours from satellites an estimate of how much it rained. For the vegetation data we can see globally every day, if there are no clouds, how productive the vegetation is. Is it green or is it wilted⁷ or is it dry?”

What Beck and his colleagues found was that when enough rain has fallen there’s a “surge in the greening of grasses.”

Beck said, “We do see that rainfall is what gets them going. That was very clear. But then, once they’re on the move, they appear to rely both on rainfall and the productivity of vegetation because the leg of migration we looked at is at the end of the dry season. So when we look at the vegetation that’s surrounding them and how green it is, really, we can tease out how fast the animals will migrate.”

And they’ll follow the greening vegetation. But Beck said the zebras are in tune⁸ with the environment and don’t simply move blindly in one direction.

“If the rains then abate⁹ or you get an interruption, then they’ll actually reverse their migration, which is something that had only very rarely been documented. They’ll reverse their migration and wait for the next spell of rains. Same thing when they return from the very productive grasslands¹⁰ where they are in the wet season. If you get a very late rain spell, they’ll actually reverse again and extend the period that they can graze in the grasslands,” he said.

So researchers wanted to know whether being in tune with their environment would help the zebras – and possibly other migrating animals -- adapt to climate change.

Beck said, “In our research we assessed the chance of those weather systems becoming decoupled and really the cues that animals rely on now not becoming reliable anymore in the future – and whether the animals’ behavior is adaptable¹¹ enough to cope with that.”

That kind of knowledge could help in the conservation of wild animals. He also says knowing which migration routes animals will take may help game park rangers¹² and others better protect them from poachers. Beck and his colleagues presented their findings in the Journal of Geophysical Research – Biogeosciences.

1 migration   

n.迁移，移居，（鸟类等的）迁徙

参考例句：

• Swallows begin their migration south in autumn.燕子在秋季开始向南方迁移。
• He described the vernal migration of birds in detail.他详细地描述了鸟的春季移居。

2 trek   

vi.作长途艰辛的旅行；n.长途艰苦的旅行

参考例句：

• We often go pony-trek in the summer.夏季我们经常骑马旅行。
• It took us the whole day to trek across the rocky terrain.我们花了一整天的时间艰难地穿过那片遍布岩石的地带。

3 delta   

n.（流的）角洲

参考例句：

• He has been to the delta of the Nile.他曾去过尼罗河三角洲。
• The Nile divides at its mouth and forms a delta.尼罗河在河口分岔，形成了一个三角洲。

4 migrations   

n.迁移，移居( migration的名词复数 )

参考例句：

• It foundered during the turmoils accompanying the Great Migrations. 它在随着民族大迁徙而出现的混乱中崩溃。 来自辞典例句
• Birds also have built-in timepieces which send them off on fall and spring migrations. 鸟类也有天生的时间感应器指导它们秋春迁移。 来自互联网

5 conserving   

v.保护，保藏，保存( conserve的现在分词 )

参考例句：

• Contour planning with or without terracing is effective in conserving both soil and moisture. 顺等高线栽植，无论做或不做梯田对于保持水土都能有效。 来自辞典例句
• Economic savings, consistent with a conserving society and the public philosophy. 经济节约，符合创建节约型社会的公共理念。 来自互联网

6 buffalo   

n.(北美)野牛；(亚洲)水牛

参考例句：

• Asian buffalo isn't as wild as that of America's. 亚洲水牛比美洲水牛温顺些。
• The boots are made of buffalo hide. 这双靴子是由水牛皮制成的。

7 wilted   

（使）凋谢，枯萎( wilt的过去式和过去分词 )

参考例句：

• The flowers wilted in the hot sun. 花在烈日下枯萎了。
• The romance blossomed for six or seven months, and then wilted. 那罗曼史持续六七个月之后就告吹了。

8 tune   

n.调子；和谐，协调；v.调音，调节，调整

参考例句：

• He'd written a tune,and played it to us on the piano.他写了一段曲子，并在钢琴上弹给我们听。
• The boy beat out a tune on a tin can.那男孩在易拉罐上敲出一首曲子。

9 abate   

vi.(风势，疼痛等)减弱，减轻，减退

参考例句：

• We must abate the noise pollution in our city.我们必须消除我们城里的噪音污染。
• The doctor gave him some medicine to abate the powerful pain.医生给了他一些药，以减弱那剧烈的疼痛。

10 grasslands   

n.草原，牧场( grassland的名词复数 )

参考例句：

• Songs were heard ringing loud and clear over the grasslands. 草原上扬起清亮激越的歌声。 来自《现代汉英综合大词典》
• Grasslands have been broken and planted to wheat. 草原已经开垦出来，种上了小麦。 来自《简明英汉词典》

11 adaptable   

adj.能适应的，适应性强的，可改编的

参考例句：

• He is an adaptable man and will soon learn the new work.他是个适应性很强的人，很快就将学会这种工作。
• The soil is adaptable to the growth of peanuts.这土壤适宜于花生的生长。

12 rangers   

护林者( ranger的名词复数 )； 突击队员

参考例句：

• Do you know where the Rangers Stadium is? 你知道Rangers体育场在哪吗？ 来自超越目标英语 第3册
• Now I'm a Rangers' fan, so I like to be near the stadium. 现在我是Rangers的爱好者，所以我想离体育场近一点。 来自超越目标英语 第3册