This episode of the InsideNATURE podcast is all about sloths–perhaps the strangest group of creatures evolution has ever produced. While other species get ahead by being the fastest, the biggest or the strongest, sloths do everything as slowly as possible, using the least amount of energy and remaining largely unnoticed. But don’t be deceived by their low-key lifestyle. Sloths have been around millions of years, much longer than humankind, so they must be doing something right.
To guide us through the weird and woolly world of sloths, we reached out to biologist Rebecca Cliffe. Her research focuses on sloth conservation and she has taken an innovative approach–utilizing tiny sloth “backpacks”–to study the ins and outs of their daily life.
Listen to the podcast interview above or read an edited transcript that follows.
NATURE: You’re working on your PhD in conservation biology at Swansea University in the UK and your main subject of study is sloths. Aside from the fact that they are adorable, is there another reason that you chose to study sloths?
I find them fascinating because they’re so unusual and so unlike any other mammal, yet we know so little about them. As a budding biologist, I find it really fascinating that there is an animal out there, which is doing everything in a different way than we expect, and yet we really have no idea how they’re managing it; how they’re managing to live a life which is on the edge of what we think is possible.
NATURE: Why haven’t sloths been studied very much?
You think they’d actually be quite an easy study subject because they don’t move that much. You’re not chasing a cheetah around the plains of Africa, after all. However, as I started to follow wild sloths around, I soon discovered that once they go up into the trees, you can’t do any observations on them whatsoever. If you’re lucky, you’ll get a glimpse of them every now and again. If you want to know what they’re eating and how much time they’re spending in different behaviors, you can’t see that with your eyes. Up until recently there just hasn’t been the technology available in order to do that electronically either. It’s really just recently that we’ve been able to start to understand what it is that they’re doing.
NATURE: In 2013, you raised $95,000 online to study the movements of sloths by outfitting them with little backpacks that contain GPS trackers and other information gathering devices. Could you tell us what you hoped to achieve with that study and do you have any results to share ?
That study, the Sloth Backpack Project, is still ongoing. I wanted to attach not only tracking devices, but data loggers to wild sloths. When you’re putting a data logger on an animal it is hard to use it in a collar format because the collar can twist around and you never know which direction the animal is facing. That’s where the whole backpack idea came from because it held everything nicely against the animal’s back. Whenever it moved or whenever it did anything we could have the data logger record it. The data loggers are recording GPS points so we know exactly where the sloth is, but they’re also recording every time the animal moves, every time it chews, every time it climbs down the tree or up the tree and we have pressure sensors so we know how high the animal is.
There are also temperature sensors and light sensors so we know whether he’s basking in the sunlight or curled up in the shade. You can really put together exactly what the wild sloths are doing and where they’re doing it. That is key to understanding their ecology. What I wanted to get out of all of this research is to help the conservation of the species. It’s difficult to conserve an animal that you know is suffering in the wild, when you don’t know what the species needs in order to survive.
NATURE: Sloths sort of have a reputation for being cute but also lazy and not very intelligent. Is that representation accurate? And does your data from this tracker study back that up in any way?
When sloths were first discovered they were described in the literature as the lowest form of existence. They didn’t really get off on a very good foot. They were thought to just sleep all day. I’ve heard things like they sleep for 23 hours a day or they can spend an entire week and not move. Because people have never been in the field to observe them, nobody knows whether that’s true or false. They’ve just got stuck with this lazy stigma and everyone believes it because it’s sort of a nice story. What we’re actually finding out is that sloths don’t sleep that much at all. They only sleep for about 13 hours a day. I know some humans who sleep more than that! I really don’t think they deserve the lazy title. The rest of the time they are moving but they’re just doing everything really, really slowly, which people also think is lazy because they can’t be bothered to move faster.
Actually, it’s an amazing way to survive. When you don’t have the energy or physical capability to run away from a predator then you have to rely on them not seeing you in the first place. What they are doing is basically stealthily creeping through the trees. The predators just don’t notice them. If predators don’t notice them that means that humans haven’t noticed them either. We think that they just sit around and do nothing all day, but actually they’re moving. They’re just going completely under the radar.
NATURE: Moving slowly is also a way for them to save energy, correct?
Yeah, if you’re moving slowly you don’t need much energy. You can survive by having a really slow metabolic rate and you don’t need to eat very much on a daily basis. You don’t have to run around looking for food like monkeys do, for example. You can afford to spend more time just taking it slow, moving slowly through the branches because there’s no rush. They get very, very little energy from their food. They survive on basically what we thought was probably impossible for any animal. A sloth is somehow managing to make it work.
NATURE: It seems like a strange lifestyle and a strange adaptation from an evolutionary standpoint. Are there other animals that exhibit this kind of behavior? Are sloths unique in the way that they eke out a living?
There are other animals that have taken the camouflage route. Sloths have just taken it to the extreme. There are animals like the koala for example who act in a similar way. The howler monkey in Central America, they’re very similar to the sloth in that they have the same diet and they’re about the same size, but they’ve gone in the opposite direction. The howler monkeys have energy to run away from predators, but in order to maintain that energy they have to eat a ton of leaves every single day. They spend all day eating, eating, eating. They actually sleep for 18 hours a day. Nobody thinks that they’re lazy because they see them rushing through the canopy. Sloths, on the other hand, eat the same food, but just not very much of it and just stay very quiet and very peaceful at the same time.
NATURE: They must not have to eat very much, is that right?
They eat very little. It’s actually about 17 grams of dry weight of leaves a day, which is basically nothing. It’s like a clump of leaves a day. A leaf has very little energy in it. As you’ll know if you’ve ever eaten a salad, you get hungry again straight away. The sloths’ key is that they spend 30 days digesting just one leaf, so they take every nutrient possible out of that leaf. They’ve got this constantly full stomach of digesting leaves and they don’t physically have room to eat very much either. It’s not like they could just eat loads of leaves and get loads of energy if they wanted to. They physically can’t.
NATURE: So they’re being very efficient—just doing it very, very slowly.
Exactly, I think there’s a lot we can learn from them. (Laughs)
NATURE: A more recent study, which you also crowdfunded is designed to look at sloth genetics. Apparently, the Sloth Sanctuary of Costa Rica, who you’ve worked with, has seen quite a few sloths with birth defects. Could you talk a little bit about that and what might be causing them?
I noticed this when I very first went to Costa Rica and started working at the Sloth Sanctuary. They had some baby orphan sloths that had deformities. Some of them were very mild, like missing fingers or partial albinism (patches of bright white fur). Others were more severe. I’ve seen them with completely missing limbs or missing ears and deformed jaws. As a biologist, when you’re seeing that many deformed baby sloths in one rescue center at one time, that’s not a good sign. It means that there’s a lot more sloths out there being born with deformities that are never being found or are going to different rescue centers. Sloths breed very slowly. They only have one baby every three years. If so many are being born deformed, then it’s a pretty big sign that there’s something wrong in the population. I wanted to find out what it was.
From my experience in the jungles of Costa Rica, I’ve seen the effects that habitat fragmentation is having. That can be on a small scale, like a road being built through the jungle. Or it can be on a large scale with towns, cities and fruit plantations and things. As soon as you break up that continuous forest canopy, the sloths have a big problem because they don’t like to come down to the ground. You end up with these little pockets of sloths that we think are inbreeding. It’s created this very low level of genetic diversity and one of the symptoms of that is babies being born with birth defects.
It’s not quite as straight forward as that because these are also all occurring in an area which has a lot of agriculture going on. We think it is also a symptom of pesticides being sprayed in the area. There is probably a link between the two where the pesticides are creating the genetic mutations and the inbreeding is amplifying them and making them become a big issue a lot quicker.
We’re working on that with the genetics. We’re almost there with the samples and we’re starting to piece together the picture. We’re hoping within the next month we’re going to have those results. We took hair from sloths all over Costa Rica from many different populations and we’re comparing the diversity in the different regions to try and identify the ones that are most at risk, the most vulnerable areas. Then we can start to develop conservation strategies to help mitigate the situation.
NATURE: How many individuals are we talking about that have come into the Sloth Sanctuary with these deformities?
At the Sloth Sanctuary alone I’ve probably seen 15 over the years. I’ve been working with other rescue centers in the same region and I know they have had similar numbers. It’s a pretty big issue. In the towns of Costa Rica I’ve seen adult wild sloths with deformities as well. Usually only the minor ones like missing fingers because they’re able to survive with just a missing finger. But it is a symptom of something else going on. I was contacted by the Panamanian government a couple of years ago as well. They have a park right in the middle of Panama City with a wild sloth population that is completely isolated. In that park they’re finding a lot of baby sloths being abandoned because they’re deformed or they have albinism. That just ties in with the whole theory of it having to do with habitat loss and inbreeding as well.
NATURE: You said the DNA came from hair. How do you catch sloths to get their hair? It sounds like they’re hard enough to find, but then do you have to climb up in trees to grab them?
The hardest bit of sloth research is actually getting hold of sloths. To start, you have to find them and then you have to catch them. I did a tree climbing course to try to help with this, but I discovered by the time I got into the tree with all my ropes and my harnesses and things, the sloth had just moved to the tree next door. I was outsmarted by the sloths all the time! The best technique I found is to wait until sloths are found on the ground and then have people call and let me know. I’d come over, take the sample, and then release them again. Or, when they arrive in rescue centers we know where they come from and we can take the sample while they’re at the center and then release them again as well. It took a few years to get all the samples, but we have over 300 now, which is a pretty good number.
NATURE: At least you have speed on your side, I guess.
Rebecca : Not when I’m in the tree. (Laughs)
NATURE: You have a book coming out in September, which is all about sloths. Could you tell us a little bit about the book and its origin?
Yes, it’s a book that I’m writing with photographer Suzi Esterhas because there’s a lot of misinformation out there about sloths. Everybody thinks they’re lazy, stupid, dirty, and probably smelly. They do have very cute babies, so there’s a lot of sort of love for them as well. I’ve written the book to try and dispel some of the myths and as a way to spread a little bit of real information about the natural history of the species. Also, a lot of the proceeds from the book are going to a sloth conservation charity that we’ve set up and to help with issues such as the genetic deformities and electrocutions on the power lines, which I know are a huge threat to sloth populations. It’s got some pretty amazing photographs of all six sloth species. It’s a beautiful book.
NATURE: What is the most interesting thing about sloths that most people don’t know?
That’s such a hard question! There’s so many interesting things about sloths. I find it really interesting that sloths might look dirty and smelly and probably not very strong. It’s all of the opposite. They’re actually phenomenally strong. Even though they’re really skinny under all of that hair, their muscles are specially designed, which gives them fantastic strength. They can fall asleep just hanging from one arm at a right angle. If a human ever tried to do that we just couldn’t do it. They don’t produce any body odor whatsoever. That’s a strategy for survival. They’re really clean. They don’t have any parasites. It’s all just a big misconception. When people meet a sloth and they discover these things about them, they are always really shocked.