There are many mysteries in nature.大自然有许多神秘的事物
Mysteries are things we don't understand, such as how the Egyptian pyramids were built.神秘的事物是我们不理解的事，比如埃及金字塔怎么建成的
In fact, we are surrounded by mysteries.事实上，我们被神秘的事物围绕
What we know about the world seems like very little.我们对世界的所知似乎很少
Scientists tell us that what we see in the universe is only a small part of what is there.科学家们告诉我们，我所看到的只是宇宙中的一小部分
The rest is invisible, including dark matter and dark energy. 其它的是看不见的我，包括暗物质和暗能量
These two unknowns make up around 95% of the universe.这两个未知的大约占宇宙的95%
Evidence for their existence comes from their effects on what we can observe, such as the motion and positions of distant galaxies.它们存在的证据来自它们对我们所能观察到我事物的影响，比如遥远星系的移动和位置
Yet, though we know very little, we are able to build airplanes and communicate with smartphones.然而，虽然我们知道的很少，但我们能建造飞机和用智能手机通讯
In some ways we humans are very smart, or at least we think we are.在一些方面我们人类非常聪明，或者至少我们认为我们很聪明
We still need to face big issues, like climate change, and that is going to be a huge challenge.我们仍然必须面对大的问题，如气候变化，那将是一个巨大的挑战
The challenge for humans will be our ability to adapt to our changing environment.人类的挑战将是我们适应不断变化的环境的能力
What about other forms of life?How do they adapt? 其它生命形式怎么样？它们如何适应？
Seasonal variations, for example, can be one of the greatest challenges for animals to overcome. 季节的变化可能是动物克服的巨大的挑战之一
Overcoming such challenges is a great achievement, but hardly easy.克服这样的我挑战是一个伟大的成就，但不容易
Some birds migrate thousands of kilometers each year to deal with seasonal changes.一些鸟没年迁移数千公里去适应季节变化
These migrations are amazing.这些迁移是令人吃惊的
Birds don't carry maps or compasses, yet they know where to go.鸟类不带地图和指南针，然而它们知道去哪里
They have developed the ability to see the Earth's magnetic field.它们有发达的感知地球磁场的能力
This ability is a wonder of nature.这个能力是大自然的奇迹
It takes advantage of the fact that the earth is like a huge bar magnet.它利用地球像一个巨大的磁棒的事实
It has a north pole, which is positive, and a south pole, which is negative.它的北极是正极，南极是负极
Somehow the birds are able to see this magnetic field and use it to their advantage.奇妙的鸟类能感知这磁场和利用它的优势
How do birds know where to fly?鸟类怎么知道飞到哪里？
They use the Earth's magnetic field.它们使用地球的磁场
And even the way birds fly together is amazing.甚至鸟类一起飞行的方式也令人惊奇
Many migrating birds fly in a V formation.许多迁徙的鸟呈V 型飞行
They do this to conserve energy.它们这样做是保存能量
In a V formation, birds can use the energy of the birds in front of them.呈V型，鸟类能使用它们前面的鸟的能量
This energy comes from the air currents generated by the wings.这种能量来自翅膀产生的气流
Conserving energy is necessary for the birds to survive the long journey.保存能量对鸟类长途旅行中生存是必要的
How do the birds know this?鸟类是怎么知道这的？
It's truly amazing how the birds know this鸟类是如何知道这些的，这真令人惊奇
Another amazing example of survival is the salmon.另一个幸存的惊奇事例是鲑鱼
Salmon spend most of their lives in the ocean, which is saltwater.鲑鱼大部分生活在海洋中度过，海洋是咸水
Yet, when it's time to breed, they do so in freshwater rivers. 然而当它们到繁殖的时间，它们在淡水河里繁殖
Salmon can adapt their bodies to survive in both saltwater and freshwater.鲑鱼能使自己的身体适应咸水和淡水生存
When it's breeding time, they return to the same river where they were born.当它们繁殖的时候，它们回到它们出生的河流
it seems as if they have a built-in map that guides them for hundreds of miles.这似乎好像它们有一个内置地图指导它们走几百英里
Once they leave the saltwater, they don't eat.一旦它们离开咸水，它们就不吃东西
They are determined to finish their journey, despite the many obstacles.它们决心完成它们的旅行，尽管许多障碍
They swim against strong currents, jump over waterfalls and try to escape the claws of hungry bears.它们抵挡强烈的我水流（逆流而上）跳过瀑布，试图逃离饿熊的爪子
Many die along the way, but enough of them survive to breed and produce the next generation.许多死在沿途，但它们有足够的幸存下来繁殖下一代
Once they have laid their eggs, they die, having completed their journey.一旦它们生下它们的蛋，它们就死了，已经完成它们的旅程
It seems that their purpose in life is just to reproduce.似乎它们生活的目的就是繁衍后代的
Migration takes animals to new, more favorable environments when the seasons change.当季节变化时，迁徙把动物带到新的，更有利的环境
Some of these journeys are long and dangerous, along routes with no obvious landmarks. 其中一些旅程是很长且很危险的，沿途没有明显的地标
The longest migration is that of the arctic tern.最长的迁徙是北极燕鸥
It flies from pole to pole, twice a year.它从一个极点飞往另一个极点，一年两次
If a tern achieves its average lifespan of 20 years, the distance it has flown will be equivalent to a journey to the moon and back.如果燕鸥的平均寿命达到20岁，那么它飞的距离相当于一次往返月球的旅行
Humans also migrate, but seldom if ever for seasonal variations.人类也迁移，但是很少因为季节变换迁移
Unfortunately, human migrations are often due to human activities.不幸的是，人类迁移通常由于人类活动
Since the beginning of the 21st century, large scale migrations have become a global problem.自21世纪开始大规模迁徙已经变成全球问题
Millions of migrants have had to leave their countries and look for new homes.数百万移民不得不离开他们的国家寻找新的家
Many have died along the way or lived as refugees in camps until they are admitted into a new country.许多人死在沿途或生活在难民营，知道他们被准许进入一个新的国家
So the question remains as to how our global community will face these challenges 因此，问题仍然关于我们全球社区将如何面对这些挑战
