Three-fingered sloth ‘adopts’ a two-fingered sloth baby!

Three-fingered sloth ‘adopts’ a two-fingered sloth baby!

These two sloths are not only different species, but they belong to two completely different families, separated by over 30 million years of evolution. Cross-species adoptions like this are incredibly rare in the wild, with only 3 other documented observations of this happening.

Three-fingered sloth 'adopts' a two-fingered sloth baby
Copyright: Oscar Solano Rojas

What happened?

On the 20th December 2020, Gerald Pereira and Oscar Solano Rojas were guiding a group of tourists in Costa Rica. Sloths are a common sight on these tours, but that day they saw something that they had never seen before – nestled quietly amongst the rainforest canopy they spotted an adult three-fingered female tending to a two-fingered baby sloth.

Gerald and Oscar, both with over 11 years of experience working as ecotourism guides, knew they had witnessed something important.


Three-fingered sloth 'adopts' a two-fingered sloth baby
Copyright: Oscar Solano Rojas

The curious pair were observed in a fragmented strip of rainforest, sandwiched between a river, a pineapple plantation and a busy road. According to Oscar, “in that area, local people take great care of the sloths, so we always go to look there because there is a very large population”.

“Yesterday we started the tour, which we call the ‘Sloth Tour’, as usual. To see them active in the early hours of the day, we started the tour at 6am. Around 8am we arrived at a place where my partner Gerald and I saw a sloth hanging from a Cecropia tree. At first, it did not attract much attention, we saw that she was a female and a baby, but that morning we had already seen 3 baby sloths, and we did not think it was anything special or different from what we had seen. When we paid more attention to them, however, we discovered that it was a three-fingered female and a two-fingered baby.”

Three-fingered sloth 'adopts' a two-fingered sloth baby
Photo credit: Oscar Solano Rojas

“I had already seen the two species in the same tree many times, and at first we thought it was just a coincidence that they were there together. When we found them it seemed like they were waking up. They both started scratching, and then the baby separated from the female, fed on cecropia leaves a little, and I thought that was the end of the interaction.”

“But then you see how the baby returns to the female, and she receives it with total naturalness, that is what surprised us the most. None of us who were there could believe it, neither Gerald nor I, because we had never seen it before. It left me astonished. In rescue centres, I had seen a certain attachment between the two species, but never in their natural habitat, as happened to us yesterday.”

Three-fingered sloth 'adopts' a two-fingered sloth baby
Copyright: Oscar Solano Rojas

As can be seen in the video footage captured by Gerald and Oscar, it does indeed appear that the two sloths interact with the gentle tenderness of a mother-baby relationship. When they returned to the area the next day, they once again found the pair snuggling together in a shady spot in the canopy. It certainly looks like the bond between these two sloths is much more than just a fleeting interaction. It appears as though the female has formally adopted this baby as her own.

Three-fingered sloth 'adopts' a two-fingered sloth baby
Copyright: Oscar Solano Rojas

Odd Alliances

Adult animals adopting unrelated young is nothing new to science, but in most cases these are intraspecies interactions – meaning that they occur between two unrelated individuals of the same species. This has most commonly been observed within sociable species, often herd or pack animals.

Interspecies adoptions – where a female adopts a baby of a different species – is an altogether much rarer occurrence in the wild. In fact, there have only ever been 3 other documented instances of this happening, and it has never before been observed in sloths. 

In 2004, a group of capuchin monkeys were documented caring for a baby marmoset, and in 2014 a bottlenose dolphin adopted a baby melon-headed whale and nurtured it for it for 3 years. More recently, a lioness in India was found to have adopted an orphaned leopard cub in 2018 and she raised it alongside her own offspring.

Why do cross-species adoptions occur?

In evolutionary terms, caring for another animal’s offspring like this doesn’t make much sense. Raising a baby demands a lot of time and energy (something which a sloth has a limited supply of), and it is usually done with the purpose of propagating an individual’s own genes. So why do cross-species adoptions like this sometimes happen?

The truth is, scientists are still trying to understand it. Because these events are so rare, there isn’t much information available and each observed case appears to be very different. There are two popular theories:

  1. Instinct: A lot of adult female animals are biologically hardwired through evolution to care for helpless infants. A cross-species adoption might occur accidentally after a female has recently given birth herself, when high levels of the hormone oxytocin encourage her to bond with the orphaned baby (even if it isn’t hers!).
  • Mutual benefit: If the benefits of the raising an unrelated baby outweigh the costs, this could explain why some interspecies adoptions take place. For example, it could be beneficial for a group of animals to add a new individual that would help to secure more food, or provide added protection. In some social species the simple benefit of companionship may be a driving force! This is unlikely to be an important factor for our solitary sloths though.


Lioness, Nosikitok, nurses a leopard cub in the Ngorongoro conservation area in Tanzania
Lioness, Nosikitok, nurses a leopard cub in the Ngorongoro conservation area in Tanzania. Photograph: Joop van der Linde/AP

How did this happen?

The circumstances surrounding this adoption are not entirely clear, but SloCo founder and sloth expert Dr. Rebecca Cliffe has some ideas about what might have led to this unusual event.

“This is the first time that anything like this has ever been seen before in wild sloths, and it is certainly very interesting. I am used to sloths surprising us, but this has to be one of the most unusual things I have heard about. I suspect there are three possible scenarios which may have led to this happening:

1) Accidental human interference. Maybe someone found the baby sloth alone and tried to ‘reunite’ it with its mother, but accidentally paired it with the wrong sloth. Reuniting baby sloths with their mothers is a surprisingly common requirement for people in Costa Rica as babies are often found alone on the ground after falling from the tree.

A lot of people don’t realise that there are two very different types of sloth, and so they might not have realised what they were doing. In this situation, however, I would expect the adult sloth to reject the baby and so this feels like an unlikely scenario

Three-fingered sloth 'adopts' a two-fingered sloth baby!
Copyright: Oscar Solano Rojas

2) The baby sloth lost it’s own mother, and instinctively clung onto the fur of another sloth. Baby sloths are born with a strong instinct to cling onto mom’s fur, and if they are separated, they tend to cling onto the next best thing. It isn’t impossible to think that this baby may have climbed onto the three-fingered sloth after becoming orphaned. However, in this situation I would also expect to see the adult sloth looking agitated and stressed out by her new uninvited companion – and I doubt the relationship would last more than a few hours.

Three-fingered sloth 'adopts' a two-fingered sloth baby!
Copyright: Oscar Solano Rojas


3) The baby sloth lost its own mother, and the adult sloth recently lost a baby of her own. This unusual combination of events would provide a feasible opportunity for the pair to bond naturally due to a mixture of instincts and hormones. Although extremely rare, I think this is probably the most likely scenario!”


Three-fingered sloth 'adopts' a two-fingered sloth baby!
Copyright: Oscar Solano Rojas


What happens next?

This unprecedented behavior leaves all of us with many questions – particularly regarding the welfare of both sloths! Will the baby survive? It’s certainly possible. While they are different species, they do share a broadly similar ecology.

The diets of both sloths overlap heavily, with both being predominantly folivorous (eating only leaves). Two-fingered sloths tend to be more flexible and adaptive with their choices, while three-fingered sloths are more selective about what types of leaf they will eat. With both species, babies maternally inherit knowledge about which trees are safe to feed from – and this arrangement may work in the baby’s favor!

Three-fingered sloth 'adopts' a two-fingered sloth baby!
Copyright: Oscar Solano Rojas

Furthermore, it appears as though the baby sloth is approximately 7 months old. At this age, the baby would not be as reliant upon a steady source of milk from the mother as the natural weaning process would be taking place. Although the adult female could be producing milk, we don’t think this is essential for the survival of the baby at this stage.

Two-fingered sloths are also much larger than their three-fingered counterparts when fully grown, which means that the adoptive mother may have a challenge on her hands when lugging around her overgrown offspring.

Three-fingered sloth 'adopts' a two-fingered sloth baby!
Copyright: Oscar Solano Rojas

But what happened to the baby’s biological mother? This remains a mystery. Considering the location in which the pair were observed is highly disturbed, it may be that she got into trouble with the busy road or nearby pineapple plantation. Or perhaps there was an accidental baby mix-up, and somewhere in the rainforest, a mother two-fingered sloth is tenderly nurturing a baby three-fingered sloth. It’s doubtful we will ever know for sure.

While there are certainly a lot of challenges for this pair to overcome, here at SloCo we have high hopes for their survival. After the unprecedented global difficulties that 2020 has brought, we are happy to embrace this heart-warming story (which has all the makings of a future Disney movie!).



We will be working closely with both Gerald and Oscar to monitor the two sloths as time goes on – we will keep you updated on their progress! For now, we are keeping our fingers and toes crossed for a happy ending.

2021 Update:

It’s with a heavy heart that we must inform our supporters that the wild three-fingered sloth mom that was found to be caring for a two-fingered baby has passed away.

Local guides who were tracking the pair witnessed the mom and baby fall from their tree. Unfortunately, mom did not survive the fall. The baby was uninjured and climbed back up into the tree.

The guides continued to watch over the baby for the rest of the evening, and returned to the spot every day to check on him – but after three days he had ventured off on his own into the rainforest.

We estimate that the baby was around 8 months old, at which point he would naturally begin to distance himself from his mom. Team Sloth is optimistic that his two brilliant sloth moms taught him everything that he needs to know in order to survive in the wild!


-Sloth Team


The ‘mummified’ skin of a giant sloth proves that they coexisted with the first humans of South America

The ‘mummified’ skin of a giant sloth proves that they coexisted with the first humans of South America

Although it was on display for a long time at the Museum of La Plata, Argentina, its age was uncertain. A new study indicates that giant ground sloths lived 13,000 years ago and coexisted with the first humans of South America.

The mummified skin of the mylodon was found on a scientific expedition organized in 1899 by the Museo de La Plata (UNLP). Mylodons were an extinct genus of animals that lived during the Pleistocene, a period that ranged from approximately 2.5 million to 10 thousand years ago.

Since it was first discovered in 1899, it has remained on exhibit. The artifact is a true treasure considering its surprising degree of preservation: it still has hairs and soft parts. After extensive discussions about its age, this remarkably preserved skin lost the interest of paleontologists until recently when a group of experts resumed studying it and dated it again. This time they used sophisticated techniques that left no room for doubt: the owner of that tissue lived about 13,200 years ago. This discovery has just been published in the journal Quaternary Science Reviews.

Secretos de una joya del Museo de La Plata: científicos del CONI
Leandro Pérez, one of the researchers, next to the showcase where the skin is exhibited. Photo: courtesy of researchers.

The skin of the giant sloth

The giant sloth – the common name for this genus – was one of the largest land animals in South America, weighing more than 1 ton and measuring 3 meters (almost 10 feet) in length. It had huge claws and walked on all fours, although it is thought that it could also stand on its hind feet (bipedal). With its herbivorous habits, it was part of the South American megafauna, the large mammals that dominated the planet during the Pleistocene.

The skin was found in the Cueva del Milodon (Milodon’s cave), a natural formation located in southern Chile that was explored in the late 19th century. The cave contains countless paleontological remains, and even evidence of early human activity. At that time the geographic limits of Argentina were still being established, which allowed for expeditions of many different origins to go and collect materials. As the story goes, when Argentinian naturalist Florentino Ameghino first saw the remains, he assumed that they belonged to a living species. This led him on an impassioned quest to find a living specimen, which of course did not happen.

giant sloth skin
Photo: Courtesy researchers

“The skin is really striking: it is a centimeter and a half thick with long reddish-yellow hairs and it is hard like wood. In what would be the interior, it is covered by a ton of small bones, similar to a suit of armor, which is typical of some species of fossilized sloths,” explains Néstor Toledo, CONICET (National Council for Scientific and Technical Research) researcher on the Faculty of Natural Sciences and Museum of the National University of La Plata (FCNyM, UNLP) and one of the authors of the work.

The scientific process

First dated in 1974 with questionable results, the team of scientists sent a sample back to the same radiocarbon laboratory in the United States that had done the original analysis. They used a method to determine the age of carbon-containing materials and this time it was clear that that the sample was over 13,000 years old. The authors of the study also sent a fragment of skull bone from the same cave to an Argentinian laboratory which turned out to be 11,300 years old. This was the same age of two bone tools carved by ancient humans that were found next to the sloth hide, according to the original reports of the find.

The specialists also examined two sloth shoulder blades, one belonging to the local collection and the other belonging to the Zurich Museum of Natural Sciences. These bone pieces, which were dated between 12 and 13 thousand years old, have cut marks on made by tools and evidence of them being dragged across the ground. “This constitutes indirect evidence of human presence, that of course must continue to be studied, but it is an indisputable proof of coexistence with human beings and, if verified, it would be one of the oldest records in South America,” says Leandro M. Pérez, CONICET researcher at the FCNyM and leading author of the publication. This question takes on a special interest considering the debate on whether or not this giant fauna coexisted with these first settlers.

giant sloth skin
Photo: Courtesy researchers

In addition to the new ages obtained, the investigation includes an exhaustive review of  the dating methods of all the mylodon remains found in that same cave which appear in the scientific literature. Starting with the first of them, carried out in 1951 by Williard Libby, the winner of the Nobel Prize in Chemistry in 1960 and creator of the radiocarbon method, they verified a total of 36 records, discarding those that were unsuccessful or uncertain.

“We have taken on the monumental job of searching for each published piece of information, tracking the sample it refers to, and calling the laboratory in charge of dating it to trace a match between these references. We found some errors and we left only those reliable historical values,” ​​Pérez explains, and adds:” It is not that before they worked badly, but that the protocols that we use today did not exist at the time. For example, they didn’t understand the importance of including a photo or a drawing of a material or assigning it a catalog number in the collection.

Interesting questions

As a final reflection, the researchers highlighted two important values ​​of their work. “On the one hand, there is interest on the climatological level, since it was a time of intermittent glaciations. Despite the very harsh conditions due to the cold and the amount of ice, this cave was inhabited continuously for at least a thousand years, according to our bibliographic review. For this reason, it raises countless questions about how this fauna could have evolved, which in the case of the ancient sloths were gigantic and woolly, while their current relatives are small and live hanging from the trees in tropical jungles,” argues Toledo.

Secretos de una joya del Museo de La Plata: científicos del CONI

Pérez alluded to a second relevant question, related to “the importance of valuing the heritage we have and the way the naturalists worked at that time, people who traveled to distant and hostile places without even knowing if they would return alive. Many museums in the world have pieces from this site because they were bought from collectors. But on the other hand, very few, like ours, have materials recovered in scientific expeditions organized and led by researchers from the institution.”

carlos ameghino
Fiorentino Ameghino, considered the first Argentinian paleontologist, and team in one of their expeditions.

Mummification: yes or no?

Although there is talk of “mummified” skin, in reality it is unclear if the term exactly applies to the way the famous “sloth leather” was preserved. “It is not how one might imagine an Inca or Egyptian mummy, subjected to a series of deliberate treatments to preserve it in this way. There was no dehydration here because the cave was terribly cold and humid, and it wasn’t from freezing either.

What took place was a more complex process. Right now we are carrying out a chemical analysis on some of the microcrystal sheaths that cover each hair, that we saw through electron microscopy,” described the authors, who speak of a kind of “natural tanning.” The material was buried under a meter-thick layer of manure that was compacted, and therefore lacked oxygen. “We think that the excrement produced the release of tannins, chemical compounds that are used to tan leather, and that spontaneously triggered the process,” concluded the experts.


-By Mercedes Benialgo, CONICET La Plata

Leandro M.Pérez, Néstor Toledo, Florencia Mari, Ignacio Echeverría, Eduardo P. Tonni, Marcelo J.Toledo. Quaternary Science Reviews. Radiocarbon dates of fossil record assigned to mylodontids (Xenarthra – Folivora) found in Cueva del Milodón, Chile. DOI:


Love avocados? Thank the Giant ground sloths!

Love avocados? Thank the giant ground sloths!

Did you know that we can thank giant ground sloths for the avocados we have today? Giant ground sloths were one of the few ancient herbivores large enough to swallow avocados whole, thus serving as an important seed disperser for these delicious fruits that we know and love today!

Illustration of the giant ground sloths by Robert Bruce Horsfall/Source: Wikimedia Commons


Many plants, especially in tropical ecosystems, have evolved to rely upon animals to spread their seeds. Only extra-large herbivores such as the giant ground sloths had the ability to swallow avocado seeds whole, meaning that they could carry them around in their digestive tracts and eventually defecate them far away from the parent tree!

Evidence of these ancient symbiotic (mutualistic) relationships can still be seen today. For example, honey locust trees (Gleditsia triacanthos) have large sweet-smelling seed pods that were eaten by megafauna. They also have big, intimidating spikes on their trunks which likely served as an important defense against these giant herbivores. Now a popular city tree due to their ability to withstand poor conditions, modern versions of honey locust trees have been bred without spikes although their supersized seed pods still litter our bustling city streets.

Seed pods and thorns of the honey locust tree (Gleditsia triacanthos). Although seemingly powerless against modern tree-dwellers these spikes likely served as a vital protection against the large herbivores of the Pleistocene./Images:

How big were the giant ground sloths?

These ancient ancestors of modern-day sloths truly lived up their name. Like bears and anteaters, they had the ability to stand on their hind legs, making them the largest bipedal mammals to have existed. Over 100 species of giant ground sloths lived throughout North, Central, and South America, ranging in size from the formidable Megatherium americanum which towered 3.5 meters tall (12 feet), and weighed up to 4 tons, to the considerably smaller 90-kg (200-lb) Cuban Megalocnus. 


Skeleton of the giant ground sloth (Megatherium americanum)/Source: Wikimedia commons


The giant ground sloths of North America disappeared around 11,000 years ago and their South American cousins followed suit around 10,200 years ago. However, amazing fossil evidence from 2007 revealed that 200-lb Megalocnus were still lumbering around the islands of Cuba as little as 4,200 years ago!


Skeleton of the considerably smaller Cuban ground sloth (Megalocnus rodens)./Source: Wikimedia Commons

Why did the giant ground sloths disappear?

Like many of the memorable megafauna of the last ice age, the exact cause of their extinction remains somewhat murky. Megatherium fossils have been found with cut marks on them, suggesting that ancient humans did consume these giant beasts. However, humans and the giant ground sloths of Cuba coexisted for a period of about 1,000 years. It is likely that a combination of over-hunting and/or climate change led to their demise.


Artist’s interpretation of the giant ground sloth (Megatherium) of the Pleistocene and two Glyptodon./Source: Wikimedia commons


Although the last of the giant ground sloths disappeared around 4,200 years ago, modern sloths carry on their legacy. Scientists have hypothesized that modern-day two and three-fingered sloths evolved from two distinct lineages of extinct giant ground sloths. In other words, although not closely related, two and three-fingered sloths both evolved independently to live in trees, in a process called convergent evolution. However, recent genetic evidence suggests that the species of sloths alive today may have evolved from an ancestor that was comfortable on the ground as well as in the trees.


The future of avocados

Without their ancient seed dispersers, the future of avocados is now in our hands. Unfortunately, avocado trees are quite sensitive to changes in temperature and water. A single avocado requires 60 gallons of water to grow. Fluctuations in rainfall and temperature due to climate change are causing shortages of these lucrative crops. Moreover, the expansion of avocado farms in Mexico has led to the destruction of pine and fur forests thus affecting monarch butterflies. The high demand for avocados has even caused gang warfare to break out in areas such as the Michoacán state of Mexico, where almost 80% of the US’s avocados come from.

Also known as “alligator pears” avocados became popular due to the targeted marketing efforts of Californian farmers in the 1990s./Image:

A sustainable future for avocados means growing them in places where water is plentiful using agricultural methods (such as agroforestry) that make space for biodiversity.


-Katra Laidlaw



Five-ton giant sloth lived in Costa Rica seven million years ago!

Five-ton giant sloth lived in Costa Rica seven million years ago!

A giant sloth weighing five tons and whose height could exceed twice that of a human being was part of prehistoric Costa Rica seven million years ago.

A group of paleontologists is working hard to determine the characteristics of this giant sloth to see if it corresponds with previously described species – or whether it is completely new to science!

This is part of a project that started in 2003 in San Gerardo de Limoncito, Coto Brus, about 11 kilometers from San Vito. In this area, the researchers searched for bones and fossils of different species.

For more than a decade, Ana Lucía Valerio, coordinator of Geology at the National Museum, and César Laurito from the National Institute of Learning (INA) searched and analyzed more than 2,600 samples of bones from dozens of different species that appeared throughout the expeditions.

giant sloth
The bones found correspond to giant sloths similar to those in this image, whose height can easily exceed twice that of a person. Illustration: Franklin Rodríguez

“When I decided to go for paleontology, no one cared for something to appear here. Venturing out to find mammals was unthinkable. They told us ‘you are looking for little bones, it is not important, but the finding makes the world look again and say ‘something is happening here, something we did not expect and that is changing the vision of biological exchange'” Laurito explained.

This region is important because it provides further proof that Central America served as a bridge for animals to cross from South America to North America and vice versa. 

“We are talking about something very old. The Isthmus only closed about 3.5 million years ago, but these sloths lived seven million years ago. So how did these giant animals from South America get to southern Costa Rica if they had no adaptations for swimming? It is possible that for a time there was a pass, a land bridge, for these animals to cross. This passage could exist for a short period of time, but for paleontology, a short period of time could be a million years ”

“In other words, species from South America are appearing much earlier than expected – by about four million years” he clarified.

Describing the sloths:

In recent years, Valerio and Laurito have described many different species of prehistoric horses, camels, armadillos, and other types of mammals on Costa Rican soil.

However, they had a problem with the sloths’ material as they had no way to compare it. This type of research in paleontology is very new in Costa Rica, and so they formed a collaboration with Ascanio Rincón, head of Paleontology at the Venezuelan Institute of Scientific Research, who has been studying these prehistoric giants for many years.

Rincón helped to complete the next part of the analysis: determining what kind of sloths they are. All of the bones were found at the same site, but they accumulated during different years of searching.

“There is no record of these animals in North America until much later. What prevented them from crossing? Or what did they find here that made them stay longer without moving?” Rincón wonders.

For this new analysis, all bones must be photographed, measured, analyzed, described and compared with the bones of other giant sloths. After all of this, important aspects of these populations can be determined.

giant sloth found in costa rica
The Venezuelan paleontologist Ascanio Rincón (left) is in the country to collaborate with the research of Ana Lucía Valerio Zamora and César Laurito Mora, who have spent years studying the paleontology of fossils found in Coto Brus. In the photograph, they present the ankle bone of a giant sloth. Photo: Rafael Pacheco

“Now we have to do the hard work, which is to compare it with the rest of the 14 or 15 genera that exist and determine who it resembles the most and who it resembles the least and see if we are dealing with a new species,” said Rincón.
This is not easy. It is very difficult to find complete bones and so they only have small samples from which to draw conclusions.

“This is not how it looks in the movies. Not that it was just brushed off a bit and there it all appeared. We had to chop very hard rocks to be able to remove this. It took a lot of strength, a lot of searching, and sometimes bones of some species appeared, while sometimes other bones of other species. What we have today was put together and gathered over several years ”, Laurito indicated.

Rincón added: “It is hard to be able to know what is happening with only 15% of the body; how to put this puzzle together? In this case, we do have material from various types of bone that help us to better understand the panorama”.

The researchers reported that at least three individual sloths have been found as they discovered three bones of the same type but different sizes (ages). This indicates that these giant sloths may have traveled in a herd or as a family.


giant sloth
These are some of the giant sloth bones scientists are analyzing. Photo: Rafael Pacheco

What do we know about this animal?

Although it is difficult to properly visualize what these extinct sloths looked like, scientists do have some ideas!

For example, it is known that they walked on the soles of their back feet and on the knuckles of their hands. The front claws were very strong and were probably used for digging. Furthermore, due to their massive size and weight, these sloths probably did not climb trees!

Their teeth were so strong they could feed on wood and other hard materials. These teeth had a remarkable ability to regenerate from the wear and tear that was incurred when chewing. In fact, chewing was essential to prevent the teeth from overgrowing and causing problems!

Giant sloths are known to have been social animals, possibly living in large herds or family groups.


Giant Ground Sloths lived in North and South America and went ...

The importance of the discovery

Within these discoveries, there could be now-extinct species that are new to science.

“The fossil hunter does not kill his prey, he resurrects it. We resuscitate that dam that we are looking for in order to get to know it and for people to know it” said Rincón.

Why is this important? Rincón was emphatic: “This type of knowledge helps us to understand who we are, where we came from, and it gives identity to the Isthmus. We cannot judge a book by its last page, we must see what comes before, and that is why it is necessary to study paleontology ”.

-Source: Diario La nación Costa Rica

Know your Sloth Predators: The Mighty Jaguar

Know your Sloth Predators: The Mighty Jaguar

Known for their impressive hunting abilities, jaguars (Panthera onca) are both feared and revered. Weighing a hefty 56-96 kg (120-200+ lbs) they are the biggest felines living in the Western Hemisphere and the third largest cat species on Earth (after lions and tigers).

Boasting one of the most powerful bites in the animal kingdom, their name comes from the indigenous word “yaguareté” which means “true, fierce beast” or “he who kills with one leap.”

So what do jumping jaguars and stealthy sloths have in common?  They are more intertwined than first meets the eye.

Sloths and Jaguars

Like most apex predators, jaguars are also a keystone species, helping to maintain a balanced ecosystem by keeping herbivore populations in check. Jaguars are opportunistic hunters, and prey upon almost anything they can get their jaws on. To name a few, they eat capybaras, deer, tortoises, iguanas, armadillos, fish, birds, and monkeys.

They even have the ability to take down South America’s biggest mammal, the tapir, and catch an equally formidable predator, the caiman.

Unfortunately for sloths, they are also on the list. Sloths have evolved their stealthy habits to remain hidden from their main predators jaguars and harpy eagles, who rely on their sense of sight to find them. If discovered, the sloth’s remarkable grip strength helps them to survive an attack by avoiding being pulled from the trees by these powerful predators.

They are both threatened by habitat fragmentation

Like sloths, jaguars are particularly vulnerable to the effects of habitat fragmentation, especially on the grand-scale. Although, jaguars have been sighted as far north as the deserts of Arizona their range of six million square km (over 2,316,000 square miles) extends from northern Mexico through Central America into Northern Argentina.

historic current range of jaguar
Although jaguars are widespread, their total population is estimated to be only 173,000./Image:

Jaguars require large amounts of primary rainforest in order to survive. A study that monitored the activity of jaguars in Southern Mexico using GPS collars, determined that a female jaguar used at least 180 square km over the course of a year and a male jaguar had a home range of 430 square km. A healthy population of 500 jaguars could require anywhere from 153,250-192,400 square kilometres (approximately 60,000-75,000 square miles)!

The jaguar’s main stronghold is the Amazon basin, with half of the world’s population of jaguars living in Brazil. In South America, the historic range of the jaguar has been reduced by half and overall jaguar populations are decreasing.


jaguar corridor panthera mesoamerican
In addition to protecting large swaths of jaguar habitat, Panthera aims to connect these areas through preserving and restoring and biological corridors./Image: Panthera

Although protected areas are key to their survival, maintaining and restoring connectivity throughout their range is essential for the health of the species. Reknowned jaguar scientist Alan Rabinowitz (1953-2018), known for establishing the first jaguar preserve in Belize in 1986, was particularly concerned about this issue. In 2006, he co-founded Panthera to protect jaguars and other wild cat species across their ranges.

Since jaguars require such vast amounts of intact forest, they are also known as an umbrella species. Conserving jaguars benefits a variety of other species, including sloths.

They are both hunted

In addition to habitat loss and fragmentation, one of the main threats to jaguars is poaching. Although sloths are protected in many places where they are found, they are still hunted. The endangered maned sloth in Brazil is particularly threatened by hunting.

Jaguars are victim to two main kinds of hunting: revenge killing and poaching to sell jaguar parts on the black market. Hunting jaguars out of revenge usually occurs after a jaguar has killed livestock. Fortunately, organizations such as Panthera, reduce conflict between jaguars and people by implementing a variety of anti-predator strategies, such as putting livestock in enclosures at night.

Surprisingly, the most sought after parts of the jaguar are their canines, which are used to make jewelry or traditional Chinese pseudo-medicine.

Sloth and Jaguar coats are designed for camouflage

Sloths and jaguars are both interested in staying camouflaged, although for opposite reasons! Sloth fur has specialized grooves along the shaft of each hair and microcracks which help to trap moisture and promote the growth of algae and fungi.

The algae and fungi growing on the sloth will eventually turn the sloth green, a perfect disguise for an animal that seeks to blend in with the canopy of a tropical rainforest.

Jaguars’ coats are also designed for camouflage. Like other spotted cats, their rosettes help them to camouflage and enable them to remain hidden while sneaking up on unsuspecting prey.

jaguar camouflage
The rosettes of the jaguar help them to blend into their surroundings./Image:


jaguar leopard difference
Although jaguars are sometimes mistaken for other big cats, such as leopards, their spot pattern is quite unique with small dots inside of their rosettes./Image: The Wildlife Diaries.

They both have unique mating calls

When a female three-fingered sloths is in heat, she will call out (in the key of D sharp) to let males in the vicinity know that she is ready to mate. Since sloths are not known for their speed, she can call out for several days before a male sloth finally reaches her.

Jaguars are among the four species of big cats that can roar. To communicate during the breeding season, both male and female jaguars will roar to each other, which sounds like the sawing of wood.

They both have impressive teeth

Although their diets differ quite a bit, both two-fingered sloths and jaguars sport some pretty intimidating teeth.

Despite their peaceful reputation, two-fingered sloths have remarkably sharp teeth. Their teeth are also constantly growing, meaning that their upper teeth rub against their bottom ones in a way that grinds them down and sharpens them. Although their sharp teeth are not used to tear meat, they are useful for biting through tough leaves with ease.

sloth teeth canines two-fingered
This is why you don’t want to get too close to a two-fingered sloth/Image:

Jaguars have the strongest bite force of any big cat relative to their size.  Powerful jaw muscles paired with a shorter jaw enables the jaguar the leverage and the strength to pierce the skull of their prey.  The jaguar’s remarkable jaw strength and impressive canines allows them to bite through even the tough skin of caimans.

They are both great swimmers

Jaguars are one of the few cats that willingly go into water. Since they live in tropical rainforests, they need to be able to cross bodies of water in order to access all the parts of their habitat. The jaguar’s excellent swimming skills allow them to navigate rivers and prey upon the animals that live in them.


Sloths are also surprisingly good swimmers. Their stomachs, which are often full of fermenting gases, help them to float as they swim across open bodies of water. Male pygmy three-fingered sloths (Bradypus pygmaeus) will swim to follow the mating call of a female sloth.

They are the stuff of legends

Due to their elusive natures, sloths and jaguars are hard to study in the wild. GPS collars and well-placed camera traps have given us a glimpse into the lives of these fascinating creatures but myths still abound about both of them.

There is still so much we don’t know about sloths. Because of their curious attributes, a variety of myths have emerged about them. There was even a Greek God of slothliness.

Jaguars were revered by many ancient Mesoamerican cultures. Associated with light and dark, the jaguar’s duality was worshiped by many ancient civilizations. The Mayans believed that their keen night vision enabled them to move between worlds, and they were associated with death and the Underworld.

black jaguar cub melanistic
“Black panthers” are not a separate species but the result of extra melanin in the coats of jaguars and leopards./Image:

In order to effectively conserve jaguars and sloths, we must come to understand them. Scientists and concerned citizens continue to shed light on the behavior and habitat requirements of sloths and jaguars, which is essential information for us in learning how to live peacefully alongside them.

But beyond our understanding, these curious creatures deserve to be appreciated for their unique qualities and protected as integral parts of tropical ecosystems.

-Katra Laidlaw

With a little help from my friends: sloth hair, moths and algae

With a little help from my friends: sloth hair, moths, and algae

Sloths are naturally solitary animals, but they are not all alone up there in the canopy. In fact, sloths have an entire ecosystem living in their fur made up of different species of algae, fungi, moths and insects. That’s millions of organisms for company!

Sloth hairs have a unique structure that involves microcracks. These microcracks create the perfect environment for algae and fungi to thrive.

sloth hair friend
Three-fingered sloth hair under a microscope! You can see the microcracks and green algae. 

The microorganisms living in these cracks were investigated by biologists for the first time in 2014, and they discovered species of algae and fungi which have not been found anywhere else in the world!

These fungal species are currently being investigated by microbiologists, parasitologists, and oncologists alike, as some strains are showing uses in treatment for malaria, chagas disease, and even breast cancer.

sloth friend algae
Different strains of green algae found in sloth hair.


Good friends that provide camouflage against visual predators

Sloths have a mutualistic ectosymbiotic relationship with the ecosystem growing on their backs. The fungi, algae, and moths greatly benefit from this relationship as they have a habitat to thrive in. The sloth benefits because these organisms are key to the sloth’s best defense against predation – camouflage.

Hunters that use their sense of sight, such as raptors, will often bypass sloths when searching for prey because the growth of algae and fungi give the sloth’s fur a green tinge, allowing them to blend into the rainforest canopy. This, along with the sloth’s slow movement and other creepy crawlies that make their home in the sloth’s fur, means that sloths usually go undetected by predators who hunt by sight.

sloth selfie distance
Sloths blend in perfectly with the trees they live in.

Sloths smell like the jungle

But what about the predators that hunt by scent? Sloths don’t produce any body odor at all! The growth of this ecosystem in their fur means that sloths look like the trees, they smell like the trees and they even move like the trees (very slowly). 

sloth moths
Sloths look and smell just like the jungle that surrounds them. / Photo: Suzi Eszterhas

Sloth moths

Sloth fur is also the perfect home for six different species of sloth mothsBradypodicola hahneli, Cryptoses choloepi, Cryptoses waagi, Cryproses rufipictus, and Bradypophila garbei.

These moths are exclusively found living in sloth fur and can coexist together on the same sloth. Studies have shown that generally, the three-fingered sloth carries more moths than a two-fingered sloth, with one study recording more than 120 moths in a three-fingered sloth’s fur.

sloth friend moths
Sloth moths are unique to sloth fur! /Photo: Suzi: Eszterhas

When the sloth descends from the canopy once a week to go to the toilet, the moths will crawl from the sloth’s fur onto the fresh sloth poop to lay their eggs. This is the ideal place for these eggs to hatch, as the larvae are coprophagal which means they feed on the sloth poop. Once the larvae develop into moths, they will fly up into the trees to find an appropriate sloth to call home. And thus, the cycle begins again.

Without the sloth, these moths could not exist. The sloth gives these creatures a home and provides them with food – moths have a proboscis rather than a jaw, which they use to suck up the moisture from the sloth’s eyes and secretions from the sloth’s skin.

poop sloth moths
A sloth will only poop on the ground – a ritual that sloth moths have taken advantage of! 

The circle of life!

Sloth moths can sometimes also attract unexpected visitors. Recent footage has emerged from Cahuita National Park, Costa Rica, showing a juvenile Capuchin monkey picking and eating the moths from the fur of a two-fingered sloth! 

This incredible sight had never been captured on film before, and it is not a behaviour that we were aware of! How often does this happen in the canopy while no humans are around to watch? Something similar has also been observed with a brown jay picking the moths from the fur of a three-fingered sloth!

So, if you ever see a green sloth covered in moths, know that that is a very healthy sloth with lots of ‘creepy crawlie’ friends!

Sloth Genetics: a surprising twist

Sloth Genetics: a surprising twist

Six years ago, SloCo Founder Dr. Rebecca Cliffe launched a major research project into sloth genetics in Costa Rica. She started this project because she was concerned with the number of wild sloths in the South Caribbean region that are being born with debilitating birth-defects (missing fingers/toes, malformed ears, and misshapen limbs), and she wanted to know what was happening.

The results of this project have now been published and they reveal an unexpected situation with far-reaching implications for future sloth conservation and rescue efforts.

Cover image created by Dr. Chloe Robinson 
sloth genetics hair sample
Dr. Rebecca Cliffe, a sloth biologist, collecting hair samples from an anesthetized three-fingered sloth for a similar genetic study. Photo by Suzi Eszterhas


In order to find out what is really going on, we collaborated with Dr. Chloe Robinson, Swansea University and the Sloth Sanctuary of Costa Rica to undertake the first exploratory investigation into sloth population genetics in Costa Rica.

We collected hair samples from 98 two-fingered sloths (Choloepus hoffmanni) that originated from different regions throughout Costa Rica and used microsatellite analysis to look at the population genetics.

Infographic by Dr. Chloe Robinson


We made 3 important discoveries regarding sloth genetics:

Finally, after many years of hard work, we are delighted to announce that the results of this research have now been published as an open-access article in Evolutionary Applications. We have summarized the results below.

We were able to identify 4 genetic groups of two-fingered sloths in Costa Rica (this is similar to having 4 genetic origins). If you are familiar with Costa Rican geography, these are the groups that we identified:

  • The West – sloths from the San Jose region
  • The North – includes sloths from areas surrounding Guápiles and further North
  • The East – sloths from within Limón city and surrounding areas
  • The South East – the South Caribbean region ranging from Bananito down to Manzanillo and BriBri.


sloth genetics costa rica


It is important to note that there are probably many more groups than the four that we identified, but for logistical reasons we could not collect samples from sloths spanning the whole country. Our results only reflect the areas where we were able to focus our sampling efforts.

1) Sloths in the North are genetically distinct.

Sloths in the ‘North’ group were found to be genetically very distinct when compared to the other populations. This means that sloths in this region are substantially different from sloths in other areas of Costa Rica that we sampled. We suggest that it may be important to recognize this sub-population as a separate unit for management and conservation purposes.

A distinct sub-population like this is sometimes referred to as an Evolutionarily Significant Unit (ESU).


Figure taken from the publication. Terrain map of sample sites in Costa Rica where 98 individual Choloepus hoffmanni sloths were hair sampled for genetic analyses.


2) Sloths in highly urbanized areas are inbreeding.

Sloths in the ‘West’ group have higher levels of inbreeding, (when individuals who are closely related reproduce). This may not be surprising when we consider that sloths here are restricted to living in severely fragmented forest pockets within the highly urbanized San Jose region.

This suggests that we need to focus more conservation and research efforts in this region to better understand the long‐term effects of habitat fragmentation.

sloth genetic deformities
This baby sloth was born with just one digit on each limb. The survival rate of individuals like this is very low.

3) Sloths have been moved around by humans.

Finally (and perhaps most importantly), we discovered that sloths in the West, East and South East groups were all surprisingly similar. This close relatedness between sloths living on opposite sides of Costa Rica is an unexpected and potentially concerning result. Particularly when we consider the vast geographical distance between these populations and the inability of sloths to travel long distances.

Interestingly, sloth populations in the South Caribbean were found to be more genetically diverse and had high levels of admixture (which means lots of sloths from lots of different origins have been reproducing with one another).

All of this points towards the translocation of sloths by humans in Costa Rica, where individuals have been removed from their areas of origin and released somewhere else.


sloth genetics costa rica

How could this happen?

When we consider that approximately 3 – 4 sloths are admitted into rescue centers every single day in the South Caribbean, it is not surprising that some of these animals may have originated from further away.

The translocation of wildlife was particularly prevalent in earlier years when there were not as many rescue centers who knew how to properly care for sloths. The government of Costa Rica (and in one case a national airline) would regularly deliver inured sloths from all over the country to the Sloth Sanctuary on the Caribbean Coast as they were considered to be the only experts in sloth rehabilitation at the time.

This has since changed. In the last decade there has been an explosion of new rescue centers. Costa Rica now has more rescue centers per square mile than any other country, with over 250 registered facilities currently rescuing and rehabilitating wildlife! The current abundance of rescue centers means that the cross-country translocation of sloths may be less of a problem, but the regulation of release protocols is more difficult.


Is this mix-up of sloth genetics a bad thing?

We do not know, but it could be.

You may think that high levels of genetic diversity are considered to be a good thing in wildlife conservation – and this is true. Increased genetic diversity means less inbreeding has occurred and gives populations a stronger ability to adapt when faced with change.

However, as with most things, it is rarely that simple. Mixing individuals from different genetic backgrounds can also have a dangerous effect on the health and viability of populations through a process called ‘outbreeding depression’.

loss of local adaptations


Animals often have unique genetic adaptations that help them to survive in the particular environment in which they live. For example, sloths that live in cold montane regions have adaptations to cope with a colder climate, including longer, thicker, and darker hair compared to their lowland counterparts. By moving individuals around, these adaptations can be lost and the inter-breeding that occurs can negatively impact the health of these populations.

A similar situation was recently discovered in orangutans that were reintroduced to the wild from rescue facilities in Borneo without knowledge on the genetic background and subspecies status of the individuals.

In line with this, there is an emerging global awareness of the need to consider the genotypes of animals prior to release, including official guidelines and recommendations set out by the International Union for the Conservation of Nature. However, in Costa Rica, there are currently no existing protocols or legislation to encourage or regulate this practice.

Sloths living in lowland tropical rainforests have different features compared to sloths of the same species that live in mountainous regions / Photos: Suzi Eszterhas

What does all of this mean for sloth conservation?

The genetic diversity between separate sloth populations have emerged over the course of millions of years. By mixing together populations that perhaps haven’t been in contact for millennia, we are potentially causing irreparable changes.

It may be that inter-breeding sloths from different genetic origins has no negative effects at all. But what if it does? Suddenly, we will have inadvertently compromised the viability of wild sloth populations and no amount of conservation work can ever reverse that damage. 

Is it worth the risk?

This discovery means that rescue facilities in Costa Rica should consider the genetic background of rehabilitated sloths when planning future reintroductions. Sloths should be released in the areas where they originated from whenever possible.

This will undoubtedly present a challenge for overburdened and underfunded rescue centers. Combined with increasing pressure for post-release monitoring, it may seem impossible for animals to be returned to the place of origin and simultaneously tracked to ensure survival.

Furthermore, it may not be possible to always return an animal to the place that it came from. There may be a lack of suitable habitat in that area, or the rescue center may not have accurate records on where the animal was originally found (rescued animals often pass through several pairs of hands before arriving at a rescue facility, and tracking down the origin can sometimes be difficult).


What can we do moving forward?

There will be no convenient solution, but we must work together to find one.

Ultimately it is going to require increased government assistance, funding and collaboration between different rescue centers and release sites throughout Costa Rica. It will require increased transparency and improved record keeping in order to ensure that rescued sloths are returned to where they were found. 

Furthermore, it will require the preservation of habitat where these distinct sloth populations are living (since they cannot be brought elsewhere).

When sloths were first being transported around the country, we didn’t know better. Now we do. Equipped with this new knowledge, we can now ensure that our actions to help them will truly lead to a long and healthy future for sloth populations in Costa Rica.


sloth genetics


~ Dr. Rebecca Cliffe

Founder and Executive Director 

8 Facts You (probably) Didn’t Know About Sloths’ anatomy

8 Facts You (probably) Didn’t Know About Sloths’ anatomy

What is the skeleton of a Sloth like? What are their claws made of? The internet is full of ‘facts’ about sloths. You will be surprised to know how much of this information is untrue.

For example, many people believe that the leading cause of death in sloths is when they fall out of the tree after mistaking their own arms for tree branches. This ‘fact’ was actually invented in the book ‘A Hitchhikers Guide to the Galaxy’ and is definitely not true. Because so little is known about sloths (and much of what we do know is admittedly bizarre), people are eager to believe whatever nonsense they hear or read on the internet

Here we bring you eight surprising things that you (probably) didn’t know about sloths!

1- Do sloths have nails? Or are their claws made of bone?

Well, it’s somewhere in between. While sloth claws look like overgrown nails, they are actually formed by elongated and curved distal phalange bones protruding from their limbs. These bones are covered by a sheath of the same material that makes up our fingernails and hair (keratin).

Three-fingered sloth skeleton showing the claws/fingers.

Sloth claws achieve their shape and sharpness by constant use climbing trees. If they get broken or damaged, sloths can actually regrow their claws thanks to their low metabolic rate (in a similar way to when reptiles regrow their limbs). However, the claws will rarely regain their original shape, often growing back deformed. In the wild, this can put the sloth at a great disadvantage as their claws are vital for life in the canopy.

facts sloth toed finger nails Suzi Eszterhas
A two-fingered sloth with deformed fingers from a previous injury. Photo: Suzi Eszterhas

In captivity sloths often have overgrown claws which curl painfully into the pads of their hands and feet, making climbing and feeding difficult. In these cases, the underlying bone is the same size, but the fingernail sheath is overgrowing because it isn’t being worn down by climbing as frequently or as intensely as their wild counterparts. Overgrown claws are much easier to break, and this is why sloths living in captivity often have damaged or deformed claws!

Sloths in captivity often have overgrown nails on their fingers and toes

2- There is a Greek Sloth Goddess

The Greek goddess Aergia (pronounced AIR-gee-a) is the personification of inactivity or slothliness. She guards the Court of Hypnos in the Underworld, alongside the Gods of quietness and forgetfulness. As she is the goddess of laziness, she spends most of her time sleeping and has servants do her work for her.

Unfortunately, wild sloths do not have staff to do their bidding and will only sleep 7-10 hours per day – this is around the same as a human! To put things into perspective, sloths will often share their trees with troops of howler monkeys who sleep for up to 20 hours each day.


Aergia (Greek: Ἀεργία, “inactivity”) / Image:

3- ‘Give me a lever long enough, and I shall move the world’ – Archimedes

Sloths are often described as ‘nothing but bone, skin, and fur’ which is not inaccurate but does gives the wrong impression of our robust friends. An adult sloth is approximately three times stronger than the average human, which is the result of some clever anatomical architecture.

Skkiny sloth facts suzi eszterhas
Sloths are very skinny underneath their thick fur! Photo: Suzi Eszterhas

The sloths’ evolutionary mantra has been to reduce energy consumption in every possible way – more muscle requires higher energy consumption; as a result, sloths have 30% less muscle mass than other similar-sized mammals. The fibers of these muscles are organised differently from ours, being arranged at an angle rather than parallel to the length of the muscle, which makes their muscles pound-for-pound more powerful than ours.

strong sloth
A sloth can fall asleep while dangling from a tree branch /Photo: Suzi Eszterhas

What does Archimedes have to do with this? The anatomical organisation of the muscles themselves also contributes to their disproportionate strength. Sloth muscles appear to work on a sort of lever system – resulting in an immense volume of pulling strength with very little muscle mass and expending very little energy.

facts nails
Even tiny babies are super strong!

4- Sloths can pull but they can’t push

Sloth muscles are specialized for suspensory ‘upside-down’ locomotion; they produce strong pulling and gripping motions, with very little strength for pushing. This is one reason why sloths cannot walk across the ground like a quadruped; the muscles responsible for ‘pushing’ can not produce enough force to lift their bodies off the ground for efficient locomotion (not to mention their claws also make this very difficult) and it takes an enormous amount of energy which the sloth cannot afford to lose.

Sloth road
Sloths move on the ground with a crawling motion, rather than walking / Photo: Suzi Eszterhas

This is a similar concept to a crocodile’s bite force – they have incredible force in closing their jaws, but even a strip of tape is enough to prevent them from opening their mouths.  In an ideal environment, sloths would never have to travel in this way, however, due to deforestation, they are having to come down to the ground more and more often.

5- Two-fingered sloths have black fangs

Sloths are hypsodonts, meaning that like rabbits and horses, their teeth grow continuously throughout their lives. The two-fingered sloths have four razor-sharp pseudo-canines, two on top and two on the bottom. The slight overbite causes the top pair to grow in front of the bottom pair and constantly rub against each other. Every time a two-fingered sloth opens its mouth their fangs sharpen up, maintaining two pairs of very sharp teeth.


As their diet consists of only leaves, they also ingest a lot of tannins. Tannins are the substance that gives dead leaves their brown color and will turn rivers orangey-brown during certain seasons. Sloths do not have the protective enamel layer over their teeth as we do, so the high concentration of tannins dyes their top fangs black, however, their bottom pseudo-canines remain white due to the constant rubbing against their top teeth.

Sloth teeth skull
Sloths are equipped with big teeth and they like to use them!

6- Three-Fingered Sloths have more neck vertebrae than a giraffe.

From humans to giraffes, to mice: all mammals have seven neck (or ‘cervical’) vertebrae. There are only a couple of mammals who are exceptions to this rule – sloths and manatees. Three-fingered sloths have nine cervical vertebrae, while both two-fingered sloths and manatees have only five.

sloth neck vertebrae

Now, if you are blown away by these facts and choose to do your own research, there is a debate as to whether the three-fingered sloth has eight or nine cervical vertebrae, and whether the two-fingered sloth has five or six. This discrepancy is due to a dispute on what differentiates neck vertebrae from thoracic vertebrae.

These extra cervical vertebrae allow three-fingered sloths to turn their heads through 270° which, following the sloths’ evolutionary effort to reduce energy consumption wherever possible, is a clever energy-saving tactic.

sloth turns head 270
A three-fingered sloth can see the world the right way up, despite being upside down! / Photo: Suzi: Eszterhas

No one is too sure of the evolutionary purpose of two-fingered sloths having only 5 cervical vertebrae, however, it has been suggested that this abnormality allows two-fingered sloths to tilt their heads all the way backward. This can be useful when trying to access hard-to-reach leaves on the tips of branches!

Sloths utrning their heads facts

7- Sloths can float thanks to their stomachs

A sloth’s torso is two-thirds stomach. This very large, four-chambered stomach is mostly full of gas from fermenting leaves, which acts as a floatation device. There is a common myth that it is impossible for a sloth to drown because of this gassy stomach (which is not true), but these built-in floaties are certainly an advantage in the water.

Three-fingered sloths are very good swimmers. In fact, they can travel three times faster in the water than on land! It has been suggested that the sloth’s extra cervical vertebrae help to help keep the sloth’s nose above water while swimming. 

sloth floating
A Pygmy three-toed sloth swimming in a mangrove forest Isla Escudo de Veraguas, Panama / Photo: Suzi Eszterhas

8- Ribs… ribs…. ribs… and some more ribs

Unlike vertebrae, the number of rib pairs in mammals varies between species. If you take a look at the two-fingered sloth skeleton pictured, you can see that there looks to be a disproportionate number of ribs – there are 21 pairs! This is the largest number of ribs in any mammal, with humans having 12 pairs and whales only having nine!

In all animals, rib cages function to protect our internal organs. A sloth’s stomach can occupy up to 30% of the sloth’s body weight – a stomach this large needs some extra support and protection! Sloths regularly fall from the canopy (they can fall from 100 feet in the air and survive!) and so having tough internal hardware is important! 


Approximate size and location of the sloth stomach /Photo: skull unlimited

Three-fingered sloths also have multiple unique fibrinous adhesions that effectively anchor their abdominal organs against the lower ribs. These evolutionary ‘coat hangers’ support the weight of the sloth’s stomach and bowel whilst the animal is hanging inverted, preventing the lungs from being squashed and facilitating breathing.

-Amelia Symeou

Ecology Coordinator


Did you enjoy these facts?

Genética de perezosos: un giro inesperado

Genética de perezosos: un giro inesperado

Hace seis años, la fundadora de SloCo, Dra. Rebecca Cliffe, lanzó un importante proyecto de investigación sobre la genética de perezosos en Costa Rica. Este proyecto se inició debido a la cantidad de perezosos salvajes en la región del Caribe Sur que nacen con condiciones genéticas debilitantes (falta de dedos en manos y pies, malformaciones en orejas y extremidades deformes).

Los resultados de esta investigación ya se han publicado y revelan un escenario inesperado, con implicaciones de largo alcance para futuros esfuerzos de conservación y rescate de perezosos.

sloth genetics hair sample
Dr. Rebecca Cliffe, bióloga con especililización en perezosos, recolectando muestras de pelo de un perezoso de tres dedos bajo anestesia para un estudio genético similar al presente/ Photo: Suzi Eszterhas


Con el fin de averiguar qué está sucediendo, colaboramos con la Dra. Chloe Robinson, la Universidad de Swansea y el Sloth Sanctuary para llevar a cabo la primera investigación exploratoria sobre la genética de la población de perezosos en Costa Rica.

Recolectamos muestras de pelo de 98 perezosos de dos dedos (Choloepus hoffmanni) de diferentes regiones de Costa Rica y utilizamos análisis de microsatélites para observar la genética de la población.

genetica perezosos

Hicimos 3 descubrimientos importantes con respecto a la genética de los perezosos:

genetica perezosos

Finalmente, después de muchos años de arduo trabajo, nos complace anunciar que los resultados de esta investigación ahora se han publicado como un artículo de acceso abierto en Evolutionary Applications. Hemos resumido los resultados a continuación.

Pudimos identificar 4 grupos genéticos de perezosos de dos dedos en Costa Rica. Si está familiarizado con la geografía costarricense, estos son los grupos que identificamos:

  • Oeste: perezosos de la región de San José.
  • Norte: incluye perezosos de áreas que rodean a Guápiles.
  • Este: perezosos de la ciudad de Limón y sus alrededores.
  • Sureste: la región del Caribe Sur, desde Bananito hasta Manzanillo y BriBri.

genetica perezosos costa rica

Es importante señalar que probablemente hay muchos más grupos que los cuatro  identificados en este estudio, pero por razones logísticas no fue posible recolectar muestras de perezosos en todo el país. Nuestros resultados sólo reflejan las áreas en las que pudimos enfocar nuestros esfuerzos de muestreo.

1) Los perezosos del área Norte son genéticamente distintivos.

Se encontró que los perezosos en el grupo ‘Norte’ eran genéticamente muy distintos en comparación con las otras poblaciones. Esto significa que los perezosos en esta región son sustancialmente diferentes de los perezosos en otras áreas de Costa Rica que muestreamos. Sugerimos que reconocer a esta subpoblación como una unidad separada puede ser importante para fines de manejo y conservación.

Una subpoblación distintiva como esta podría considerarse una Unidad Evolutiva Significativa.


Gráfico tomado de la publicación original. En el mismo se aprecian los puntos de muestreo.

2) Los perezosos en áreas altamente urbanizadas presentan endogamia.

Los perezosos en el grupo ‘Oeste’ tienen niveles más altos de endogamia (cuando individuos que están estrechamente relacionados se reproducen). Esto puede no ser sorprendente si consideramos que los perezosos aquí están restringidos a vivir en parches de bosque severamente fragmentados dentro de la región altamente urbanizada de San José.

Esto sugiere que debemos centrar más esfuerzos de conservación e investigación en esta región para comprender mejor los efectos a largo plazo de la fragmentación del hábitat.

sloth genetic deformities

3) Los perezosos han sido translocados por humanos.

Finalmente, y quizás lo más importante, descubrimos que la genética de los perezosos en los grupos del Oeste, Este y Sudeste eran sorprendentemente similares. Esta estrecha relación entre los perezosos que viven en lados opuestos de Costa Rica es un resultado inesperado y potencialmente preocupante. Particularmente si tenemos en cuenta la gran distancia geográfica entre estas poblaciones y la incapacidad de los perezosos para trasladarse largas distancias.

Curiosamente, se descubrió que las poblaciones de perezosos en el Caribe Sur eran más genéticamente diversas y tenían altos niveles de mezcla (lo que significa que muchos perezosos de muchos orígenes diferentes se han estado reproduciendo entre sí).

Todo esto apunta hacia la translocación geográfica de los perezosos por parte de los humanos en Costa Rica, donde los individuos han sido retirados de sus áreas de origen y liberados en otro lugar.

genetica de perezosos costa rica

¿Cómo pudo pasar esto?

Cuando consideramos que aproximadamente 3 -4 perezosos son admitidos en centros de rescate todos los días en el Caribe Sur, no es sorprendente que algunos de estos animales puedan haberse originado desde más lejos.

La translocación de la vida silvestre fue particularmente frecuente en los años anteriores cuando no había tantos centros de rescate que supieran cómo cuidar adecuadamente a los perezosos. El gobierno de Costa Rica solía entregar regularmente perezosos de todo el país al Santuario de Perezosos en la costa del Caribe, ya que se los consideraba los únicos expertos en rehabilitación de perezosos en aquel momento.

Esto ha cambiado desde entonces. En la última década ha habido una explosión de nuevos centros de rescate. Costa Rica ahora tiene más centros de rescate por kilómetro cuadrado que cualquier otro país, con más de 250 instalaciones registradas que actualmente rescatan y rehabilitan la vida silvestre. La abundancia actual de centros de rescate significa que la translocación de perezosos a través del país puede ser un problema menor, pero la regulación de los protocolos de liberación es más difícil.

¿Es esta mezcla genética algo malo?

No lo sabemos, pero podría serlo.

Generalmente, los altos niveles de diversidad genética se consideran algo bueno en la conservación de la vida silvestre. El aumento de la diversidad genética significa que se ha producido menos endogamia y esto brinda a las poblaciones una mayor capacidad de adaptación ante el cambio.

Sin embargo, como con la mayoría de las cosas, rara vez es así de simple. Mezclar individuos de diferentes orígenes genéticos también puede tener un efecto peligroso sobre la salud y la viabilidad de las poblaciones a través de un proceso llamado “depresión exógena”.



Los animales a menudo tienen adaptaciones genéticas únicas que los ayudan a sobrevivir en el entorno particular en el que viven. Por ejemplo, los perezosos que viven en regiones montañosas tienen adaptaciones para hacer frente a un clima más frío, que incluye un pelaje más largo, más grueso y más oscuro en comparación con sus contrapartes de las tierras bajas. Al mover individuos de un lugar a otro, estas adaptaciones pueden perderse y el entrecruzamiento puede afectar negativamente la salud de estas poblaciones.

Esta situación se descubrió recientemente en los orangutanes que fueron reintroducidos en la naturaleza desde instalaciones de rescate en Borneo sin conocimiento sobre los antecedentes genéticos y el estado de las subespecies de los individuos.

En línea con esto, existe una conciencia global emergente de la necesidad de considerar los genotipos de los animales antes de la liberación, incluidas las directrices y recomendaciones oficiales establecidas por la Unión Internacional para la Conservación de la Naturaleza. Sin embargo, en Costa Rica, actualmente no existen protocolos o leyes existentes para alentar o regular esta práctica.

Los perezosos de las tierras bajas tiene características diferentes a los perezosos de su misma especie que habitan las zonas montañosas./ Photos: Suzi Eszterhas


¿Qué significa todo esto para la conservación de los perezosos?

La diversidad genética de las poblaciones separadas de perezosos ha surgido en el transcurso de millones de años. Al mezclar poblaciones que tal vez no han estado en contacto durante milenios, podríamos estar causando cambios irreparables que se perpetuarán por generaciones.

Puede ser que los diferentes orígenes genéticos de estas poblaciones no tengan efectos negativos en absoluto. Pero ¿y si lo hacen? En tal caso, habremos comprometido inadvertidamente la viabilidad de las poblaciones de perezosos salvajes. Llegado a ese punto ningún esfuerzo de conservación podrá revertir ese daño.

¿Vale la pena el riesgo?


Este descubrimiento implica que los centros de rescate en Costa Rica deberían considerar el trasfondo genético de los perezosos rehabilitados al planificar futuras reintroducciones. Los perezosos deben ser liberados en su área de origen siempre que sea posible.

Sin duda, esto presentará un gran desafío para los ya sobrecargados centros de rescate con fondos insuficientes. Combinado con una presión cada vez mayor de monitoreo posterior a las liberaciones, parece imposible que los animales regresen a su lugar de origen y además se les rastree para garantizar su supervivencia.

Además, puede que no sea siempre posible devolver siempre un animal al lugar de donde vino. Puede haber una falta de hábitat adecuado en esa área, o el centro de rescate puede no tener registros precisos de dónde se encontró originalmente al animal. Esto se debe a que los animales rescatados a menudo pasan por varias manos antes de llegar a una instalación de rescate, y rastrear el origen del individuo a veces puede ser difícil.


Entonces, ¿qué podemos hacer?

No existe una solución fácil, pero debemos trabajar juntos para encontrar una.

En última instancia, se requerirá una mayor asistencia y financiación gubernamental. También será necesaria la colaboración entre diferentes centros de rescate y sitios de liberación en todo Costa Rica. Se requerirá una mayor transparencia y un mejor registro para garantizar que los perezosos rescatados sean devueltos a donde fueron encontrados.

Además, es menester la preservación del hábitat donde viven estas poblaciones distintivas de perezosos, ya que no se deberían liberar en otro lugar.

Cuando los perezosos eran transportados por todo el país, no sabíamos las consecuencias que esto podría traer. Ahora lo sabemos. Equipados con este nuevo conocimiento,  podemos asegurar que nuestras acciones para ayudarlos realmente conducirán a un futuro saludable para las poblaciones de perezosos en Costa Rica.




Endangered Sloths

Endangered Sloths

You may be surprised that only two of the six species of sloths are considered threatened with extinction by the International Union for Conservation of Nature (IUCN), who the vast majority of the scientific community consider having compiled the most comprehensive and reliable information source of population counts and risk levels facing flora, fauna, and fungi.

There has never been a more important time for conservation action, with a UN report declaring that over 1 million species are now at risk of extinction. The loss of species and habitats now poses as much danger to life on Earth as climate change does.


habitat loss
Banana plantation in the Caribbean of Costa Rica / Photo credit: Kra Ya

Species are classified by IUCN according to their conservation status, ranging from Least Concern to Extinct, by assessing:

  1. ·       The rate of population decline
  2. ·       Changes in geographic range
  3. ·       Whether the species naturally possess a small population size 
  4. ·       Whether the species naturally has a small geographic range
  5. ·       Whether the results of a quantitative analysis indicate a high probability of extinction in the wild

Reasons for the decline of sloth populations

Ultimately the decline of sloth populations is due to deforestation and urbanization, which have resulted in a multitude of risks for sloths. Due to habitat loss sloths are coming down to the ground more frequently, and are therefore vulnerable to dog attacks, car strikes, and poaching.

sloth problem


With canopy fragmentation, sloths are using powerlines to move around, which easily leads to electrocutions, and in areas where rainforest fragmentation is so severe genetic bottlenecks are occurring.


electrocutions sloth
Over half of the electrocuted animals in Costa Rica are sloths


The maned and the pygmy sloth

The difference between these guys and the other four sloth species is that the Pygmy and Maned Three-Fingered sloths are endemic, only existing in small areas, thereby have a small population due to their limited geographic distribution. The Two-fingered species and other two Three-fingered species have considerably larger habitat ranges, so while the destruction of the rainforest and constant urbanization of sloth habitats affects all sloths, the effect is far more profound on these much rarer animals.


1. The Maned Sloth


maned sloth


The maned sloth is a bit of an oddball – a species of three-fingered sloth that boasts a mane like a lion! These elusive creatures (which look remarkably like a coconut with a mullet) now only exist in a tiny strip of Atlantic forest on the coast of Brazil and are currently listed as vulnerable.



There is also some evidence to show poaching for both food and the pet trade are contributing to the problem. The maned sloths are larger and more aggressive than the other species of three-fingered sloth, and they are the only species in which males do not develop a brightly coloured “speculum” (an orange patch of fur on the back) at sexual maturity!


Maned sloth

Why is the maned sloth considered an endangered species?

The maned sloth is declared ‘vulnerable´ mainly due to its restricted geographic range, resulting in the canopy fragmentation and urbanization effects having more immediate and dramatic results on the individuals as well as the population.

 The known populations of Maned Sloths are in restricted and discontinuous regions in Brazil (Bahia, Espírito Santo, and Rio de Janeiro). Their estimated area of occupancy, based on the remaining forest within its range, is less than 1,000km2.


maned sloth


It’s unknown how many individuals of maned sloths are left in the wild. They are much shyer, and so well camouflaged to their environment that SloCo founder, Dr Rebecca Cliffe, spent two weeks searching for these guys and only caught a glimpse of one. More research is required about population size, distribution, and trends, life history, ecology, among other aspects of the species (keep your eyes peeled for some exciting SloCo news regarding this!).

2. The Pygmy Sloth

The second endangered species on our list is the pygmy sloths. These are the smallest (and cutest?) species of three-fingered sloth and can only be found on a remote, uninhabited island off the coast of Panama. They were only identified as a new species in 2001 and are most famously known for their swimming abilities.


pygmy sloth
Pygmy sloth swimming / Photo credit: Suzi Eszterhas


They are thought to be approximately 40% smaller than their mainland counterparts and although the population size remains unknown, these little sloths are considered to be one of the most critically endangered mammals in the world. They average around 3 Kg in weight and are approximately 24 inches long, looking very similar to the brown-throated sloth.


Pygmy sloth

Why is the pygmy sloth a critically endangered species?

According to UICN ‘Endangered (EN), is a designation applied to species that possess a very high risk of extinction as a result of rapid population declines of 50% to more than 70% over the previous 10 years (or three generations), a current population size of fewer than 250 individuals

The Pygmy Three-Fingered sloth inhabits a much smaller area the Maned Sloth – the area of Escudo Island is only slightly more than 4km2!

According to the last official account made in 2012, there were only 79 individuals left on the island.


pygmy sloth
Pygmy sloth / Photo credit: Suzi Eszterhas

We can still protect these sloths!

While this is shocking, we still have good reason to be optimistic. Every single person has the power to save endangered species. The way that each of us shops, eats, and the small choices that we make in our everyday lives all influence the likelihood of many species surviving. Please don’t ever underestimate the collective impact of your daily actions!

If you would like to know what YOU can do to help save sloths from extinction, we have compiled a list of 7 simple ways that you can help sloths today!

If you would like to make a gift to support our work during these uncertain times, any contribution is greatly appreciated. Donations, symbolic sloth adoptions, and merchandise purchases all help us in our mission to protect sloths.