In search of the pygmy sloth

A group of tiny sloths living on an uninhabited island will finally be accounted for, after a team of conservationists from the Zoological Society of London (ZSL) conducted a census of the pygmy three-toed sloth (Bradypus pygmaeus).

The team undertook a nine-day expedition to Escudo Island, 17km off the coast of Panama, which is the only place in the world where the sloths are found. There, they conducted a population and habitat survey of the area covered by mangroves, and spent time monitoring the unique behaviours of the world’s slowest mammal.

At half the size of their mainland cousins, and weighing roughly the same as a newborn baby, pygmy sloths are the smallest and slowest sloths in the world. They are ranked at number 16 on the EDGE of Existence mammals list and remain critically endangered.

ZSL’s David Curnick says: “Very little is known about this species. Current population estimates are, at a best guess, fewer than 500, but this is only based on anecdotal evidence. We’ve collected data to get a more accurate picture of how many pygmy sloths are left in the world.”

Escudo is an unpopulated island fringed by mangrove forests, and roughly the size of New York’s Central Park. As well as sloths, it is known to be home to several other endemic species, including the neotropical fruit bat (Artibeus incomitatus) and the maritime worm salamander (Oedipina maritime), but very little is known about its wildlife, and the island remains largely unexplored.


As well as using bromeliad leaves as an umbrella to protect themselves from extreme weather, pygmy sloths appear to use mangrove trees as a tool to regulate their body temperatures – on cooler days they climb to higher spots to catch the sun, and when they get too hot they head down again to find a shadier spot.

The team’s current data suggests that there could be fewer than 100 pygmy sloths left, making them one of the most endangered mammals in the world. The exact reasons for the sloth's threatened status are not yet known, but they found several areas where their critical mangrove habitats have been cut down.

Dr. Craig Turner added: “The mangrove forests are relatively hard to penetrate, and from a sloth’s perspective they may provide protection from aerial predators. However, hunting, mangrove cutting and tourism are all listed as threats to these sloths and their behaviour may now be putting them at higher risk.”

Conservationists from ZSL are currently analysing their data, and hope to publish the findings in the next few months. The team hopes to appoint and train an in-country EDGE Fellow later in the year. They will continue their monitoring and work within the local communities to establish the main threats to the species and develop plans to protect them.

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