If there's one thing you know about sloths, it's that they're, well, slow. But that doesn't mean they're boring. In fact, sloths are one of the most extreme animals on the planet, and not just because they poop only once a week.
The Extreme Life of a Sloth
First of all, sloths really are extremely slow. Their top speeds clock in at just 0.25 kilometers per hour, making them the slowest mammal on the planet. According to zoologist Becky Cliffe, that's because, well, sloths can't really see.
首先，樹懶真的超級慢。牠們的最高時速只有 0.25 公里，是世界上最慢的哺乳類動物。根據動物學家 Becky Cliffe 表示，這是因為樹懶幾乎看不太到。
Sixty million years ago, they lost the ability to see. They went almost completely blind. So, in the daytime, a sloth actually can't see anything, because it's too bright. If you can't see where you're going, you can't run around, because you're going to fall out the tree.
Moving slowly may sound like a liability, especially if you're nearly blind, but being sluggish actually comes with all kinds of benefits. For one, they save an enormous amount of energy. In fact, sloths use about 90 percent less energy than the average mammal, which is vital, considering their diet is a low-energy snack consisting of leaves...with a side of leaves.
And as it turns out, being slow also helps sloths avoid detection. You see, sloths are so slow that predators like jaguars and eagles, which use movement to hunt, can't even find them. But some sloths take predator avoidance to the next level. Thanks to rare extra vertebrae in its neck, the three-fingered-sloth can turn its head 270 degrees, which allows it to smell incoming predators from almost any direction, and that's especially useful when you spend nearly all of your time motionless in a tree. In fact, sloths sleep, mate, and even give birth all while hanging upside down on a branch. And as you might expect, that requires some pretty extreme adaptations.
事實也證明，動作緩慢讓樹懶難以偵測。你看，樹懶的動作之慢，連獵豹和老鷹這些靠著偵測動靜來打獵的掠食者，都不會發現牠們。但有些樹懶的避敵技巧更為高明。多虧了脖子裡多出來的椎骨，三趾樹懶的頭部可以旋轉 270 度，讓牠們幾乎可以聞到來自四面八方的掠食者，假如整天都在樹上動也不動的話，這是個極大的優勢。事實上，樹懶無時無刻都倒吊在樹枝上，無論是睡覺、交配、甚至是生小孩。而如你所料，只有特化的構造才辦得到。
They've got special tendons in their hands, which lock into place.
And along with their long, hook-like fingernails, allow them to hang easily.
They're like a giant coat hanger.
And to combat a rush of blood to the head, which might be familiar if you've ever hung upside down...
They have special, sort of valves in their circulatory system that does actually stop the pooling of blood in the head.
But if you think that's extreme, consider this: Once a week, sloths risk their lives on a daring journey from the protective forest canopy to the ground. Their mission? To poop. And it really is risky.
We suspect about 60 percent of predator-based sloth deaths happen while they're pooping. They literally risk their life to come down to the ground.
我們懷疑有約 60% 的樹懶是在大便時被掠食者殺死的。樹懶真的是冒著生命危險來到地面。
So, they have to make it count. And boy, they really do. Sloths can lose an astonishing 30 percent of their body weight each time they go. Plus, they might get a mate out of it.
所以牠們得好好把握。老天，牠們真的大好大滿。樹懶每次外出都可以排泄掉驚人的 30% 體重。而且還有機會順便找到伴侶。
How do you find a mate if you are solitary, and you can't move very far? Well, they're gonna have to use pheromones and scent markers. I think that coming down and leaving a little pile at the base of your favorite trees is sort of like a little signpost.
But if there's one thing that really pushes sloths over the top, it's their rough fur. Sloths' fur has its very own ecosystem. Because they live in the rain forest, it's often wet, which creates the perfect environment for algae to grow and provides sloths with green camouflage. But it isn't just algae that calls a sloth's fur home. You can also find beetles, cockroaches, and a species of moth that's found nowhere else in the world except for on a sloth. And the sloths don't seem to mind one bit, but that's not all. Their fur might actually save lives. Fungi in their fur have been shown to fight breast cancer cells, and they may also have properties for fighting malaria. So, despite their slow pace, sloths are far from boring. And in some environments, they aren't even slow. I mean, look at that daredevil go.