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 it’s 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 behaviour 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.


-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:


Sloth Science and Universal Access to Information

Sloth Science and Universal Access to Information

September 28th is The International Day for Universal Access to Information (IDUAI), a day that, despite this digital age, goes largely unrecognized.

But what does this mean? And how does maintaining universal access to information have anything to do with sloths? In our quest to better understand these unique and enigmatic creatures, all information about them is valuable. Moreover, the success of the scientific method relies on open and equal access to information.



Origins of the scientific method

The tried and true scientific method, a staple of our science fairs and classrooms, has not always been around. It emerged in the 1600s, largely due to the work of Copernicus and Newton, whose theories helped us to understand the role of gravity in our solar system.



One of the key drivers behind the success of the scientific method has been the sharing of information. Studies are repeated in different contexts to see if the same results emerge and the knowledge gained from these experiments serve as the inspiration for new studies. Together we begin to chip away at the mysteries of the universe. However, despite its power, knowledge has not always been shared equally.


The first public library

The modern public library, as we know it today, is a fairly recent invention. There is evidence of ancient libraries dating back to 7 B.C.E with the oldest known library belonging to the Assyrian ruler, Ashurbanipal, however access to these collections was restricted. The first modern public library was created in 1833 in Peterborough, New Hampshire, making the Peterborough Town Library, the oldest public library supported by money from taxes.


Peterborough Town Library’s books could be accessed for free by anyone living in the town./Source:


Today, many of our libraries have entered the virtual realm and yet they continue to provide free access to a great assortment of educational materials. However, despite the importance of open access to information, many scientific journals still act as the gatekeepers.


Open-access journals

If you are a scientist who has just completed a study, your next step is often deciding whether you would like to publish your article in a traditional journal or an open-access journal. Historically, journals were only available in print form. Now in the age of the internet, many journals have opted to virtually publish their studies online.

Like public libraries, open-access journals are free and can be read by anyone with an internet connection. Seems like the best choice, right? Although publishing in an open-access journal can often lead to more visibility (since the study is readily available) there are hidden drawbacks.


The first and latest issue of the longest-running scientific journal, Philosophical Transactions (1665-present)./Source: Wikimedia Commons and


Scientists pay to publish, and readers pay to view

Unlike most other trades, scientists do not get paid to publish their work – it is actually the exact opposite. First, scientists have to find funding for their research (through grant applications, fundraising or self-funding) and do the hard work of actually completing the investigation. If the project goes well and they end up with a publishable paper, they then have to pay a scientific journal to publish it.

The publication fees are typically thousands of dollars (with the cost to publish in the highest ranking journals often exceeding $10,000 per article).

The majority of scientific journals then charge an additional fee to anyone who wants to read the paper after publication. Many universities will pay the subscription fees, making a variety of journals and publications accessible for “free” to their students. However, for an individual who is not studying at a university, a single article can cost $30+. A price that for many is prohibitively expensive.

For this reason, publishing in an open-access journal is significantly more expensive than publishing in a more traditional pay-to-view journal. Unless the scientist hoping to publish the study has these kinds of funds available, they may have to choose a more restricted access journal, or not publish the important findings from their work at all!

Paying to access scientific information is not an option for the majority of people living and working in regions that are of critical conservation importance.

There is an important overlap between areas of poverty and key areas of global biodiversity. If the people working on the ground to protect and conserve wildlife cannot access the latest scientific information due to the financial constraints (or language barriers, with the majority of scientific journals only publishing in English) then the information isn’t reaching the people who need access to it the most. 


SloCo’s commitment to open-access

Here at SloCo we believe that knowledge should be shared. Therefore all of the research that we have conducted on sloths is published in open-access journals. Our hope is that by enabling everyone access to this information, we can harness the power of collaborative science in order to more effectively understand sloths and how we can help them.


Sloth scientist and founder of SloCo, Dr. Rebecca Cliffe, fits a male three-fingered sloth (Bradypus variegatus) with a sloth backpack /Photo: Suzi Eszterhas


-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

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 (Really) Didn’t Know About Sloths

8 Facts You (Really) Didn’t Know About Sloths

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 the 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 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 to 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 skull teeth facts
By our own experience, we can tell you: you don´t want to get bitten by a sloth!

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


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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.




Return to the wild: post-release monitoring

Return to the wild: post-release monitoring

Two weeks ago, our three newest tracking subjects were released into the Cahuita National Park by the Jaguar Rescue Center (JRC). These Hoffman’s two-fingered sloths (Choloepus hoffmanni) – Marley, Nutella, and Iron – were raised at the JRC where they had arrived as orphan babies. Unfortunately, sloths are facing a number of threats in the wild which has resulted in them being the most common animal being admitted into rescue centers in Costa Rica.

baby sloth jaguar rescue center
A very young baby three-fingered sloth with a member of the nursery team of the Jaguar Rescue Center

Sloths live a very specific lifestyle which is being rapidly disrupted due to development. In an ideal habitat, a sloth would only come down from the tops of the trees to go to the toilet, spending almost their entire lives in the canopy. However, due to deforestation, sloths are being forced to find other ways of reaching sloth-friendly trees: descending to crawl on the ground, crossing roads, and using the power-lines.

a snuggle of baby sloths
A snuggle of baby sloths at the Jaguar Rescue Center

Why do sloths arrive as orphan babies to rescue centers?

The leading reason for sloths ending up in rescue centers is electrocutions. When a sloth touches a bare patch of line, they will receive a debilitating electric shock. 50% of sloths who are electrocuted do not survive. If a mother sloth with a baby holding into her fur is electrocuted, the baby often does not receive the full voltage of the electric shock and therefore has a much better survival rate than the mom – this is why Iron arrived at the Jaguar Rescue Center and had to be raised by humans.

Following electrocutions is dog attacks. Costa Rica has a large population of stray dogs, however dogs with owners are an equal threat, as dog ownership in Costa Rica and other central and South American countries differs from dog ownership in more developed countries. Dogs are not confined to their house and garden, but rather roam around town during the day in their packs. These dogs attack any wildlife they can, and sloths are frequent victims.

The medical issues arising from dog attacks are two-fold: the injuries themselves, and the secondary-infections resulting from bacteria in the canine’s saliva.  If a mother sloth is being attacked, she will curl herself up into a ball around her baby to protect them, which due to their immense strength (and in the case of the two-fingered sloth, their 23 pairs of ribs) often means the baby escapes uninjured.

sloth on power line
The mortality rate from electrocution is very high, but babies have a better survival rate than adults.

The importance of tracking animals after their release

Post-release monitoring is an important practice and the only reliable way to know if reintroduction is successful. However, it’s also important for learning more about those animals’ lives in the wild. There is still a vast amount we do not know about sloths, so any opportunity to collect data on their behavior and home range is precious. In a collaborative project with the Jaguar Rescue Center, we fitted Marley, Nutella, and Iron with radio tracking collars before their release in Cahuita National Park on the 13th of May 2020.

The day of the release at Cahuita National park

Marley, a handsome sloth

Marley stuck to his release tree until the 16th of May when he decided to move from his designated beach almond tree to a less-than-ideal coconut palm. Beach almonds are important feeder trees and Cahuita National Park has thousands of them, but Marley decided to relocate to an inedible coconut palm where the large leaves would help keep him cool (likely due to the unseasonably hot weather).

post-released sloth
Marley with his new tracking collar!

Marley (who our Field Operations Manager, Cecilia, believes to be the most handsome sloth in Costa Rica) has since been spotted in a variety of suitable trees, but he never strays far from his favorite almond tree, which is situated directly on the beach. Luckily sloths are not expected to adhere to the beach restrictions like the rest of us, so Marley unarguably has picked an ideal spot to call home.

sloth high in the tree
Marley in his favorite beach almond tree

Nutella, a friendly sloth

Sloths are creatures of habit, and while their home range has experts scratching their heads, it is known that each sloth has their own favorite few trees. Nutella has taken this very seriously and is still yet to move from the Beach Almond tree she was released in. However, on our most recent tracking session, we found her sharing her tree with a wild sloth! Wild sloths are solitary and often only interact with each other when courting a mate -perhaps we will hear the pitter-patter of tiny claws in 11 ½ months!

sloth with radio tracking collar posy-released monitoring
Nutella – looking at home in the wild,

Iron, the explorer

One may think that tracking sloths is an easy job, assuming they’ll just be near the same place they were in the day before. While for now Marley and Nutella are remaining close to their release sites, Iron had different plans. Sloths are slow, yes, but they are also determined and tenacious animals who can cover a surprising distance when they have a goal in mind.

Six days after release, we could not locate Iron and were receiving confusing signals at very high sensitivity, indicating that Iron was most likely very far away from the Beach Almond he had been spotted in the previous day. The weak signal was directing us outside the park towards the local neighborhood, concerning the tracking team that he may have found his way onto someone’s property.

sloth with a radio tracking collar post-released monitoring
The radio-tracking collar doesn’t bother the sloths at all!

Despite being released in an ideal environment away from dogs, humans and power-lines,  Iron decided he wanted a challenge. For 10 days our tracking team scoured the Cahuita neighborhood, battling radio interference from cars and homes until he was finally found in a small almond tree inside an empty holiday villa property.

The trees on the property had been searched the previous day, however, the signal had directed our team to the other side of a caiman-infested river, which they were unsurprisingly wary to cross and therefore brought an end to the day’s tracking. The following day the tracking team returned to the property and found him sleeping contently in a low almond tree. Thankfully, the owners of the property are happy to keep an eye on him for us and always know which tree he’s in when the tracking team visit. Community engagement and cooperation is essential for any conservation effort to succeed!

Post-released monitoring sloth
Iron has been getting into trouble!

A glimpse into the lives of sloths

In the eyes of the scientific community, this tracking project is a unique opportunity to learn about a poorly understood species. But moreover, this glimpse into the lives of these sloths is a rare chance for us to understand how we can be the best neighbors to sloths and other wildlife. As we join them on their journey back to the wild, there are many lessons that they can teach us. As sloths have shown us time and time again, there are many ways to thrive on this incredible planet.


post-released monitoring
A happy sloth adjusting to life in the wild!

Thank you to the Jaguar Rescue Center for rescuing and caring for these sloths until they were ready to return to the wild!

-Amelia Symeou

Ecology Coordinator

Camera traps fooled by sneaky sloths

Camera traps fooled by sneaky sloths

Camera traps and trail cameras are commonly used outdoors for wildlife research and they are now also playing an increasingly important role in the conservation and preservation of endangered species. These little motion-activated cameras have been instrumental in some of the most important conservation discoveries in recent years, including the identification of new species and providing living proof of species once thought to be extinct.

It’s a trap!

These hidden cameras are particularly useful for monitoring rare, elusive, shy and otherwise difficult to observe species in the wild. They are essentially made up of a digital camera connected to an infrared sensor that, by detecting differences in temperature, can identify objects that are both warm and moving (like an animal, for example). For this reason, camera trapping works very well for warm-blooded mammals and birds, but less well for reptiles and amphibians as their body temperature closely mimics that of the environment. When a warm animal moves in front of the infrared sensor, this triggers the camera and it will take a photograph or start recording video (or both)! These rugged cameras can be set up in the field and left for weeks at a time to capture the activity of any passing animal.

camera trap on a sloth crossing
We use camera traps to monitor the use of our sloth crossing bridges by different species

The good, the bad and the ugly…

By using camera traps like this it enables biologists and conservationists to easily collect ecological data and photographic evidence of elusive and often critically endangered species at little cost and with minimal disturbance. By remotely monitoring wildlife in this way it can allow us to spy on some of the rarest events in nature – events that just wouldn’t happen if there were any humans around. We can see exactly what animals are doing, where they are and how large the populations are. Camera traps that send real-time images via phone / satellite networks are also proving to be a very valuable tool in the fight against poaching.

Wild animals can often destroy camera traps! /


Despite the great potential that this technology offers, there are also numerous challenges to overcome when working with camera trapping. Firstly, wild animals do not always behave themselves around expensive technology. Larger species such as elephants, chimpanzees, bears and tigers are notorious for destroying camera traps if they discover them. In the Costa Rican jungle ants are also partial to building nests inside unattended camera traps, and if a spider decides to makes its web in front of the lens then you can forget any prized images. Humans can can also be equally mischievous, with camera trap theft on the rise! But perhaps the biggest problem is leaving electronic equipment outside for Mother Nature to play with. We speak from experience here. In the jungle environment we face 100% humidity on a daily basis, coupled with scorching heat and monsoon rains. Even the most waterproof cameras don’t last long. Biologists working in the tropics often resort to inserting silica or tampons inside cameras to absorb humidity!


A sloth shaped problem

We love working with sloths, but their characteristics do make life difficult. Cameras that are designed to detect warm, moving animals do not perform very well when pointed at a slow, cold sloth.

Their careful and steady movements are subtle enough to go unnoticed by the rainforests greatest visual hunters (big cats and harpy eagles) and so the motion sensors on many camera traps simply do not pick up the sloths slow movements. To further complicate the situation, sloths have a notoriously low and variable body temperature compared to other mammals. For this reason they are often likened to reptiles as their core temperature closely follows the that of the environment. For a camera that relies on detecting temperature differences, this is not ideal.

Camera traps do not detect wild sloths using our Sloth Crossing canopy bridges
Camera traps do not detect wild sloths using our Sloth Crossing canopy bridges

We have had a great deal of trouble finding a camera trap that will get triggered by a sloth in the wild. Some zoos and rescue centers have had success using camera traps within their captive exhibits, but the environment inside a zoo is very different to the rainforest. Firstly, the ambient temperature tends to be much lower in a zoo which means that the sloth appears warmer. Secondly, a camera trap placed inside an enclosure is often much closer to the action. In the tropical jungle habitat we will be lucky to get a sloth passing by within 10 – 20 meters of the camera. And finally, captive sloths living in zoos tend to move faster than a wild sloth creeping through the jungle due to a lack of fear and predators. For example, we know that wild sloths move faster at night because they are less visible to predators!

A camera trap donated by Nature Spy
A camera trap donated by Nature Spy


And finally a solution

This situation may seem ridiculous, but the sloths inability to trigger camera traps is making our work much harder. Whenever we install a Sloth Crossing canopy bridge we always install a camera trap nearby to monitor the use of the bridge by any animals. These bridges are built to help sloths safely move between fragmented habitats in urban areas (without risking death from road traffic collisions, dog attacks or poaching) – but it is difficult to know if the bridges are a success without any evidence of sloths using them!

To solve this predicament, we sought the camera trap expertise of Nature Spy:  a non-profit organisation that aims to research and protect wildlife whilst engaging local communities. They gave us a tutorial on how to optimise the chances of the camera trap triggering, and then generously donated two camera trap models that they thought might work. We currently have both of these cameras installed on Sloth Crossing bridges in the South Caribbean, and in a few weeks we will check the results. Huge thanks to Nature Spy for all of their assistance and we will keep you updated on any sloth sightings!

Releasing hand-reared orphan sloths back into the wild

Releasing hand-reared orphan sloths back into the wild

Can an orphan sloth that has been hand-reared in a rescue center survive after being released into the rainforest? As humans, can we raise that baby in a way that equips it with the survival skills necessary to safely navigate the treetops, find its own food and avoid predators? And what about the sloths internal immune-system defences: will these be strong enough after being raised in a sterile environment? There is only one way to find out, and so we are collaborating with the Jaguar Rescue Center to do exactly that!

The rehabilitation and release of orphan sloths is of increasing importance in the conservation and management of the species. In recent years there has been a rapid increase in the number of sloths arriving at wildlife rescue facilities in Central and South America, and although the species is not globally threatened, they are now recognised to be of conservation concern in Costa Rica. Sloths are requiring frequent rescue due to the loss or fragmentation of their habitat, disease, injury (often associated with traffic collisions, electrocutions or dog attacks), death of a mother with dependent young, or the necessity to relocate a sloth away from a dangerous location.

The primaryIMG_0600 aim of wildlife rehabilitation should always be to return each individual to the wild with maximum chances of survival whenever possible. A release is generally considered to be a success if the animal integrates into the wild breeding population and reproduces. The factors contributing to survival post-release are more complex for those sloths that have been orphaned and raised in captivity by humans compared to relocated or rehabilitated adults. A baby sloth is thought to stay with the mother for a full 12 months, during which time it acquires the essential skills required to survive in the wild. While many aspects of the sloth’s behaviour may be innate, certain skills must be learned. One such skill is knowing which leaves are safe to eat and where to find them, and this is a crucial lesson that wildlife rehabilitators must overcome to ensure an orphan sloth survives post-release.

To date no published studies have been carried out to determine the fate of rehabilitated, captive-reared or relocated sloths after release. Although sloths have been hand-reared and released into the wild by numerous organisations for over a decade, there has been no clear understanding of their fates because post-release monitoring with radio-telemetry has not been a common practice. This is due in part to the logistical problems associated with monitoring a cryptic arboreal species in a dense tropical rainforest, and also due to the financial burden of purchasing radio-telemetry equipment for rescue centres who receive no government funding. Consequently, there is much debate over whether hand-reared sloths can survive in the wild at all, with some institutions choosing to maintain orphan sloths as permanently captive animals to ensure their safety. With the increase in sloths arriving at rescue centres and the rapidly growing conservation concern for the species, it is becoming imperative that a standard protocol is established which enables organisations to achieve the optimum welfare outcome for each individual, whatever that may be! For sloths that do not have any physical impairments, disease or genetic problems, the ultimate goal of all wildlife rescue facilities needs to be to return these individuals back to the wild with long-term post release monitoring.


Post-release monitoring can be grouped into 3 broad data categories: survival, movement and behavioural data. While most release efforts that utilise radio-telemetry typically only monitor the length of time an animal can be located in the wild, this can often leave it difficult to determine whether an animal’s death was due to natural causes, or because the animal was not properly prepared for release. To effectively evaluate the success of a release protocol it is therefore important to combine data on the animal’s movement patterns and post-release behaviour with any changes in the overall physical condition of the animal and comparisons with similar data from wild populations.

Back to the Wild

Here at SloCo we are incredibly excited be launching a long-term collaborative study to monitor and document the survival of radio-collared hand-reared sloths after being released from the Jaguar Rescue Center (JRC) in Costa Rica.


The first 4 sloths scheduled for release were all rescued as tiny orphans (all weighing less than 600 grams) over 2 years ago and have now been equipped with VHF tracking collars and moved into the JRC’s state-of-the-art soft release enclosure.  This jungle enclosure is built over 30 meters in the air and is ideal for getting the sloths used to being up high in the rainforest canopy. The doors are scheduled to open in May 2019, and we will be tracking and reporting on the progress of these sloths for the next 2 years!