WILD LIFE | 02.20.18
Keeping Pygmy Sloths Afloat
They do almost everything else in slow motion, but Panama’s pygmy sloths are surprisingly proficient swimmers—and they find relative safety in the sea.
) takes a dip. Just discovered at the start of the 21st century, and found exclusively on this island roughly 17 kilometers (10 miles) from the Panamanian mainland, this is the only sloth known to swim in salt water. And these diminutive tree-dwellers seem to swim far more frequently than their larger cousins, placidly paddling with just their flat-snouted, hairy heads protruding from the turquoise sea.
“If they have to change trees, they just plop into the water,” says Becky Cliffe, a British zoologist and founder of the Sloth Conservation Foundation, or SloCo. “They’d rather swim than crawl on the ground.” Because sloths float easily, swimming is an efficient form of locomotion. In fact, sloths can move three times faster in the water than they can through the trees. Roughly a third of a sloth’s body mass comes from leaves in its stomach, which generate a fair amount of gas as they’re being digested. “They’re like big balls of air,” Cliffe says.
Cliffe believes pygmy sloths also likely swim longer distances than other sloths—though, like many aspects of the species’ ecology and behavior, there is no conclusive evidence.
Isla Escudo de Veraguas, Panama
What little is known only adds to the intrigue surrounding these animals. Sloths, which live only in Central and South America, belong to the order Pilosa, along with anteaters; they are also distant cousins of armadillos. Arguably some of nature’s strangest creatures, their hairy coats host entire ecosystems of invertebrates and algae; the latter lend the sloths’ coats their greenish tint. Sloths move at the astonishingly slow pace of about 36 meters (120 feet) per day, typically climbing down from their arboreal perches just once a week to poop.
Cliffe also hopes to shed light on some of the mysteries of pygmy sloths specifically—including whether they are truly a distinct species. There are six known species of sloths in total, including both two-toed and three-toed varieties. Scientists described B. pygmaeus as a new species in 2001, based mainly on its size: Pygmy sloths are roughly 40 percent smaller than the average sloth, and lighter, too, with more modest skulls. They eat the leaves of red mangrove (Rhizophora mangle) trees, which no other sloths are known to eat. And pygmy sloths live solely on Isla Escudo de Veraguas, the outermost island in the Bocas del Toro archipelago, a chain that separated from mainland Panama as sea levels rose some 9,000 years ago. Further supporting this separate-species hypothesis, Escudo de Veraguas is also home to endemic species of hummingbirds and bats.
On four of the chain’s other islands, the resident sloths are smaller than average as well. But only those on Escudo de Veraguas are different enough that scientists have designated them as a separate species. Distinct genetic differences have yet to be proven, though, and Cliffe believes pygmy sloths are actually just a smaller-bodied population of brown-throated three-toed sloths (Bradypus variegatus)—the same species found throughout Central America.
The results of the study are not yet complete, but for now the dwarf sloth is listed as critically endangered, based on its isolated habitat and what some researchers believe is a decline in numbers from hunting and potential tourism development on its island home. Although Escudo de Veraguas has no resident population of humans, indigenous families from Panama’s Ngäbe-Buglé Comarca frequently set up fishing camps there, cutting down trees for huts and firewood and purportedly eating sloths whenever their fishing nets come back mostly empty.
A scientific survey several years ago found that the island’s mangrove forests were being fragmented by tree felling, and that the resulting gaps in the canopy were interrupting the previously continuous treetop highways. This is an important loss for sloths, which are at a much greater risk of predation by feral cats, among a few other predators, when traveling on the ground.
During that study, the researchers also noted two dead pygmy sloths whose carcasses were still intact, suggesting that they weren’t killed by predators. That could signal “a high rate of death through disease, habitat loss, or natural causes,” they wrote.
“Censusing a cryptic animal such as a sloth is challenging,” wrote Bryson Voirin, a biologist at the Max Planck Institute for Ornithology, in a 2015 study of the pygmy sloth. “Standard methods such as footprint tracks and camera traps are ineffective, and visual searches likely miss an overwhelming majority of sloths, especially in the dense rainforest.” Voirin concluded that the population was far higher than previously thought, likely somewhere between 500 and 1,500.
Ongoing research continues to turn up intriguing facts about the pygmies—like what resides in the teeming cities of their fur. One team of researchers analyzed exactly what was living in the pygmy sloths’ coats and discovered that while they host just one variety of green algae, they provide habitat for nearly 40 other kinds of tiny critters—more than any other species of sloth—“including ciliates, apicomplexans, dinoflagellates, and fungi,” according to a study published in 2010.
Cliffe’s findings, when published, will provide another window into these curious creatures’ biology. And as scientists begin to see pygmy sloths more clearly, they’ll also gain new insights into how to protect the pint-sized swimmers and their lush little island home.
ABOUT THE Photographer
Suzi Eszterhas is an award-winning wildlife photographer who is best known for her images of baby animals in the wild. Her photographs have been published in more than 100 magazine cover and feature stories in publications around the world. She has ten books in print and another four in progress. She is a dedicated conservationist and lends her images and expertise to help raise funds and awareness for several environmental organizations around the world. Her latest book, “Sloths: Life in the Slow Lane” takes readers on an immersive journey through the jungles of South America to discover the secret lives of these strange and elusive creatures.
ABOUT THE Writer
Hillary Rosner is an award-winning journalist who has reported on environmental issues around the country and across the globe, for publications includingNational Geographic, Wired, The New York Times, Men’s Journal
, andHigh Country News
. She is also a contributing editor atbioGraphic
Suzi Eszterhas Hillary Rosner
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