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Most of us are surrounded by wildlife, no matter where we live.
不论住在哪里，大多数人都环绕野生动物之中。
Even in cities, we share our neighborhoods with hordes of pigeons, squirrels, and raccoons.
即使是在城市之中，我们也会和成群的鸽子、松鼠以及浣熊做邻居。
But all of those animals die eventually, right?
但是所有的动物最终都会死掉，对么？
So why aren’t we tripping over critter carcasses on a daily basis?
所以为什么我们每天都没有被这些生物的尸体给绊倒呢？
Nature, it turns out, is remarkably good at getting rid of the evidence most of the time
事实上，大自然非常擅长销毁证据
although there are some some rare exceptions that can leave us struggling to dispose of thousands of carcasses.
虽然还会有些遗漏的尸体留给我们处理。
The main reason you don't see many dead animals lying around is that most of them don't just drop dead on their own.
你没有看见动物死尸的主要原因是因为大多数动物都不会静静死去。
Unless an animal is at the very top of the food chain,
除非是生活在食物链非常顶层的动物，
it's likely that it'll meet its end at the hands or rather, claws of another animal.
否则它们很可能会死于其他动物的手下或掌下。
Pigeons, for example, rarely make it past five years old before being picked off by a predator like a hawk, owl, or stray cat.
例如鸽子，在五岁之前很少能逃过捕食者如老鹰、猫头鹰或流浪猫等的捕食。
Since these predators eat what they kill,
既然这些捕食者逮啥吃啥，
their victims are usually gone before you have a chance to see them.
那么那些死去的动物通常在你有机会看到它们前就被吃掉了。
Of course, sometimes animals do evade predators for long enough to die in some other way.
当然有时动物确实能够躲开捕食者，以其他方式死去。
They could freeze to death in a winter storm, they could starve, or they could catch a lethal disease.
它们可能会在冬季风暴中被冻死、饿死或是病死。
But even then, they don't usually just fall over in the street.
但即使是这样，它们也不会就这样倒在大街上。
Instead, they seek out a hiding spot when they feel themselves growing weak,
相反，当它们感到自己非常虚弱时，会找到一个隐蔽的地点，
crawling into someplace like a duct or a hollow tree where you're less likely to stumble across their carcasses.
爬到一个管道或是空心树之类的地方，在这些地方，你可能就无法发现它们的尸体。
And if they do die out in the open, scavengers like vultures, coyotes,
如果它们确实死在了大庭广众之下，食腐动物如秃鹰、土狼
and insects are super efficient at finding and eating them, with an assist from decomposers like fungi and bacteria.
以及昆虫能够非常高效地找到它们并在分解物如真菌和细菌的帮助吃掉它们。
Nature's cleanup crew can reduce a carcass to unobtrusive scattered bones and feathers in just a few days.
大自然的清理员可以销蚀动物尸体，仅几天时间就能够把它们的骨头和羽毛等销蚀掉。
So basically, it's not that animals aren't dying all around you all the time; it's just that you don't usually notice.
基本上并不是动物不会死在你周围，只是因为你通常没有注意到。
Sometimes, though, a large number of animals die at once -- so many that everyone notices.
有时虽然很多动物会马上死掉，多的让每个人都注意到。
In spring 2015, for example, a bacterial infection killed off more than half the world's population of saiga,
例如，2015年春天，世界上超过一半的赛加羚羊都死于一种细菌感染，
an antelope species with a funny trunk-like snout.
赛加羚羊是长着象牙般鼻子的一种羚羊。
It swept through herds in Kazakhstan, and more than 200,000 saiga died in less than a month.
细菌感染席卷哈萨克斯坦的畜群，不到一个月200,000多头赛加羚羊死去。
And in the winter of 2015 and 2016, tens of thousands of seabirds called murres washed up on the west coast of North America
2015年和2016年冬季，成千上万只海鸥被冲上了北美西海岸
after unusually warm water caused the populations of the fish they eat to plummet.
因为一场不寻常的暖水海洋导致海鸥所食的鱼类数量下降。
Events like this can overwhelm nature's capacity to dispose of the remains.
诸如此类的事件可以击败大自然处理尸体的能力。
People had to bury dead saigas in mass graves dug with bulldozers.
人类必须将这些死掉的赛加羚羊埋入推土机挖的大墓穴中。
And if it seems that things like this are in the news more and more often, you're not imagining it.
如果此类事件被报道的越来越多，你简直无法想象。
A 2015 study published in the journal PNAS found that these events are increasing in frequency,
刊登在PNAS上的一项2015年研究发现这些事件频繁增长，
becoming more common for birds, marine invertebrates, and fish.
在鸟类、海洋无脊椎动物和鱼类中越来越普遍。
The researchers followed a pretty strict definition of mass die-off,
研究严格遵循群体死亡的定义，
only looking at events that killed at least a billion animals, 635 million metric tons' worth of animals, or 90% of a population.
只考虑那些至少十亿动物、6350亿公吨重的动物或是占全体总量90%的动物死亡的事件。
The study concluded that the most common causes of mass die-offs include disease, human-caused disturbance,
研究总结到导致群体死亡的最常见原因包括疾病、人为干扰
and toxins from things like algae blooms.
以及来自其他事物如赤潮的毒素。
These events can permanently alter food webs, and they can endanger human activities like farming, too
这些事件可以永久地改变食物网，也会危及人类活动，如耕作。
for example, if there's a die-off of a crucial pollinator species.
例如，如果关键异花授粉物种的群体死亡的话。
It's unclear why this sort of thing is on the rise,
还不清楚为什么这种事件会不断上升，
but the most likely culprits are climate change and increasing environmental degradation.
但最有可能的元凶是气候变化以及大篇幅的环境退化。
Either way, scientists agree we need to do a better job of studying and tracking mass die-offs.
不管哪一种，科学家认为我们需要对群体死亡事件做大量研究和追踪。
These events are still pretty rare overall, though;
虽然总体上看，这类事件还是很稀少，
it's not going to suddenly start raining dead birds in your neighborhood tomorrow.
明天你家周围也不会突然下起死鸟雨。
And the next time you do happen to run across a smelly, rotting dead animal, remember:
下一次你偶遇发臭腐烂的动物尸体时，记住：
you have predators and scavengers to thank for the fact that this doesn't happen more often.
你要感谢那些捕食者和腐食动物，是它们让这些事不常发生。
Vultures may look kind of creepy -- but they're doing an essential job as nature's janitorial staff.
秃鹰可能看起来有些诡异，但作为大自然的清洁人员，它们做了必要的工作。
Thanks for watching this episode of SciShow, which was brought to you by our patrons on Patreon.
感谢收看本期科学秀，本期科学秀由Patreon赞助商为您呈现。
If you want to help support this show, you can go to patreon.com/scishow.
如果你想要赞助科学秀，可以登录patreon.com/scishow
And don't forget to go to youtube.com/scishow and subscribe!
不要忘记去youtube.com/scishow订阅我们的频道！
