Why Sloths Move Slow
The reason why sloths tend to move slowly on most occasions is because their metabolism is extremely slow. It takes a long time for a sloth to digest the food that is eaten, which means a sloth has to eat a lot in order to get the slow trickle of vitamins and minerals that they need. The six sloth species, which call Brazil and Panama home, move with no urgency, having seemingly adapted to an existence that allows for a life lived in slow motion. But what makes sloths so. In fact, being slow has helped sloths to survive on this planet for almost 64 million years. It is obviously a winning tactic. But in order to understand exactly what it is that makes them so slow and why it works so well, we have to look at the biology of these unusual animals in a little bit more detail. Like pacing your car when it's low on gas, sloths move slowly to conserve energy as well. In fact, they move slower than any other mammal on Earth. The arboreal animals are known for taking their sweet time getting around, usually trekking no farther than 125 feet (38 meters) in a day source: Cohn. So, the sloth’s diet makes it slow. Is that the only reason why? And isn’t it dangerous to be a slow moving creature in a jungle full of predators? Well, actually, the fact that sloths are slow actually serves as a defense. The jungles of Central and South America where sloths live are also home to some of the most fearful predators such as.
A lot of us love sloths, and one of the main reasons is we can relate to them. Just like our buddies down in the rainforest, we’d love to spend all day just hanging out (pun intended) letting the warm tropical breeze blow through our hair, at least those of us who still have hair!
Being slow is such a part of a sloth's identity, that this what their name pretty much means. (Read about that here: Is it a sin to be a sloth?)
The slowness of sloths has also inspired some great products:
Light Autumn's super sloth pun plush
But why are sloths so slow? And how do they get away with it? There are two main reasons: the sloth’s diet and its defense against predators.
Although some sloths have a varied diet, three-toed sloths are entirely vegetarians, or as scientists call them ‘herbivores’. And though human vegetarians usually eat plenty of high-energy food such as fruits and nuts, sloths subsist almost entirely on leaves, which are a plentiful food source in the rainforests where they live. I guess if you only ate lettuce you might be a bit lethargic too!
To keep their bodies functioning on such a diet, and the reason that they are so low, sloths have an incredibly low metabolic rate. In fact it is the slowest metabolic rate of all mammals. As you can see in the chart, while a sloth only uses 450 kilojoules a day, a cat uses twice as much, and humans and elephants use much, much more energy. This means that sloths can’t spend their energy darting around quickly, and instead are one of the slowest creatures around, moving on average at about 100 feet per day from branch to branch, or taking 1 entire minute to move just one foot when crawling on the forest floor. (However, because of that upper body strength and a natural buoyancy, sloths are actually the fastest when they are swimming!)
Likewise, since their diets have such little protein, and as a way to use nutrients efficiently, sloth’s bodies do not produce much muscle. Their legs are not strong enough for them to stand on them, the way humans and some primates do. So, even if sloths are on the ground they primarily depend on their arms and upper body strength to move around. So, make sure you get enough protein in your diet so you don’t wind up crawling slowly around your apartment!
Does this leave you slightly less impressed by these cute tropical tree-dwellers? Well, they aren’t just lazy salad-munchers. According to a study carried out in Costa Rica by researchers from the University of Wisconsin-Madison, sloths have something of a superpower in that they are heterotherms, meaning they can adjust their body temperature when they need to preserve energy. That’s like you dropping your body temperature down below 98.6 if you don’t get that afternoon snack.
Going back to the sloth’s diet, what they eat and how they process their food is actually quite remarkable. Although some sloths do eat some fruit and even some meat (insects and other small animals), the three-toed sloth almost only eats plants, more specifically leaves, and in particular the leaves from particular trees, namely the Cecropia tree.
You might love leafy foods like lettuce, spinach and kale, but don’t start working up an appetite for Cecropia leaves—they are extremely tough and full of toxins. Sloth may have evolved to eat the Cercropia’s leaves because most other animals avoid this plant, but in order to do so the sloth needs a special digestive system, including a multi-chambered stomach (yours just has one chamber) and special bacteria living inside the sloth to help breakdown the leaves. Even with that unique digestive system, it takes a sloth around an entire month to process its food (humans do this in about 7 hours). Another fun fact comes in at the end of that digestive process: they leave their trees and go down to the forest floor to ‘do a poo’ only about once a week!
So, the sloth’s diet makes it slow. Is that the only reason why? And isn’t it dangerous to be a slow moving creature in a jungle full of predators? Well, actually, the fact that sloths are slow actually serves as a defense. The jungles of Central and South America where sloths live are also home to some of the most fearful predators such as jaguars, panthers, ocelots, boa constrictors, anacondas and hawks. Almost all of these animals depend on their vision to catch prey. When an animal like a monkey or a parrot scurries along a branch or takes off in flight, it catches the eye of one of the jungle predators and can wind up being dinner. Since a sloth basically never makes any sudden movement it can avoid getting spotted (and eaten) by the predators of the rainforest. The next time your parents, partner, or roommates say you should get up off the couch and do something, maybe you can use the same excuse.
When sloths were first encountered by European explorers, they were given the name sloth as an accusation of being idle and lazy, but we now know why sloth seems to be lazy and it’s all about survival!
A two-toed sloth transits a plantation in northeastern Costa Rica using a cable ordinarily used to move cacao. A team of UW–Madison scientists recently found why sloths are such deliberate, slow-moving animals. Zach Peery
Although most of the terrestrial world is covered in trees, there are precious few vertebrates that make the canopy their home and subsist solely on a diet of leaves.
Tree sloths are among the most emblematic tree-dwelling mammals. However, they are best known for their pokey demeanor rather than the fact that they spend the majority of their lives in trees munching leaves. But the slow motion lifestyle of tree sloths, according to a new study, is the direct result of the animal’s adaption to its arboreal niche.
“Among vertebrates, this is the rarest of lifestyles,” says Jonathan Pauli, a University of Wisconsin–Madison professor of forest and wildlife ecology and the senior author of a report to appear in the August 2016 edition of the American Naturalist. “When you picture animals that live off plant leaves, they are almost all big — things like moose, elk and deer. What’s super interesting about arboreal folivores is that they can’t be big.”
Pauli and Wisconsin colleagues M. Zachariah Peery, Emily Fountain and William Karasov set out to measure the energetics of wild two- and three-toed sloths at a field site in in northeastern Costa Rica. The purpose of the study, Pauli says, was to help explain why arboreal folivores are indeed so rare and why more animals have not evolved to take advantage of a widespread ecological niche.
Why Does Sloths Move So Slow
A baby three-toed sloth, part of ongoing studies of the animals at a site in northeastern Costa Rica. Researchers from the University of Wisconsin–Madison have published a new report on sloth energetics, helping explain why sloths live a slow-motion lifestyle. Zach Peery
“Most of the world is forested, but the energetic constraints of a leafy diet seem to prevent adaptive radiation,” Pauli notes, referencing the canon of evolutionary biology that helps explain the diversity of life on our planet: As organisms evolve and “radiate” from an ancestral group, they take on a variety of specialized forms that enable them to live a certain lifestyle or occupy a particular niche.
The evolutionary logic of living in trees on a diet solely of leaves, it seems, is less than robust.
Sloth Predators
“Think about it,” says Pauli. “The food sucks. It’s only plant leaves. You have to exploit a very constrained niche.”
To do so, tree sloths require specialized limb adaption, reduced body mass, a slow metabolic rate and claws that act like fulcrums — hooks to accommodate the animals’ need to hang in and traverse the treetops.
“This study explains why eating leaves in the canopies of trees leads to life in the slow lane, why fast-moving animals like birds tend not to eat leaves, and why animals like deer that eat a lot of leaves tend to be big and live on the ground,” says Doug Levey, program director in the National Science Foundation’s (NSF) Division of Environmental Biology, which funded the research.
The Wisconsin group, which began the NSF-supported study in 2009, used isotopically labeled water to measure the daily energy expenditure of both two- and three-toed sloths, animals that coexist in the tropical forest canopies of Central and South America.
“It takes a suite of extraordinary adaptations to survive in forest canopies, and this may help explain the lack of species diversification among arboreal folivores.”
Jonathan Pauli
Astonishingly, three-toed sloths, which are more specialized to their environment, expend as little as 460 kilojoules of energy a day, the equivalent of burning a mere 110 calories — roughly the same number of calories found in a baked potato. It is the lowest measured energetic output for any mammal.
“The measurement was intended to find out what it cost the sloth to live over a day,” says Pauli, who explains that a diet of plant leaves has little nutritional value and the animal’s gut size limits it to small amounts per day, so the animals need to find ways to make the most of their skimpy diet. For sloths, that means expending minimal amounts of energy through a reduced metabolic rate, dramatic regulation of body temperature and navigating the world in slow motion.
The group then compared its results with similar studies of wild arboreal folivores from other corners of the globe. The take-home message, says Pauli, is that the more specialized the tree-dwelling animal, the lower the daily energy expenditure.
“The findings reinforce the concept that arboreal folivores are tightly constrained by nutritional energetics,” Pauli notes. “It takes a suite of extraordinary adaptations to survive in forest canopies, and this may help explain the lack of species diversification among arboreal folivores.”
Moving Slower Than Jokes
Tags: Costa Rica, evolution, forest & wildlife ecology, sloths