The Sloth Issue · page 6 · Hanging On

The strategy that survived the Ice Age is losing to the power line

A sloth's world is an unbroken canopy — like this one at Monteverde, Costa Rica. Everything now killing sloths is a gap in it: a road, a pasture, a wire.

Photo: Cephas, CC BY-SA 4.0, via Wikimedia Commons

The scoreboard first. Of the seven living species, four are listed Least Concern, two are Endangered, one is Critically Endangered — and all seven have decreasing populations, per their own IUCN assessments. No sloth species is doing well; some are just declining from a bigger base. Only one has ever been counted: the rest are too hard to see.

Seven species, seven downward arrows: the full sloth scoreboard

Every living sloth species with its current IUCN Red List category and assessment year. The arrow is the assessed population trend — decreasing in every case, the Least Concern species included. The maned sloth became two Endangered species in 2022, when a 172-year-old proposal was vindicated by DNA.

three-toedBrown-throated sloth Bradypus variegatusLeast Concern · 2022↓Honduras to Brazil; likely gone from Argentina — the sloth of most photographs, and of this issue's cover

three-toedPale-throated sloth Bradypus tridactylusLeast Concern · 2022↓the Guiana Shield — one rescue found 130 in a fragment of 0.07 km²

three-toedNorthern maned sloth Bradypus torquatusEndangered · 2024↓Brazil: Bahia, Sergipe — occupies 424 km², under the Endangered threshold

three-toedSouthern maned sloth Bradypus crinitusEndangered · 2024↓Brazil: Rio de Janeiro, Espírito Santo — a species since 2022 — proposed by Gray in 1850, vindicated 172 years later

three-toedPygmy sloth Bradypus pygmaeusCritically Endangered · 2022↓one Panamanian island of 4.3 km² — 2,000–2,500 animals, the only sloth with a population estimate

two-toedLinnaeus's two-toed sloth Choloepus didactylusLeast Concern · 2022↓the Guianas and the upper Amazon — found from sea level to 2,400 m

two-toedHoffmann's two-toed sloth Choloepus hoffmanniLeast Concern · 2022↓two separate blocks, Honduras to Bolivia — listed Near Threatened within Brazil

Source: IUCN Red List assessments: B. variegatus, B. tridactylus, B. pygmaeus, C. didactylus, C. hoffmanni (all assessed 2022); B. torquatus and B. crinitus (assessed 2024, published 2025). Split: Miranda et al. 2022, Journal of Mammalogy.

The edge cases

An island the size of a neighbourhood

The pygmy three-toed sloth exists on exactly one island: Isla Escudo de Veraguas, Panama — 4.3 square kilometres, cut off from the mainland for about nine thousand years, long enough for the castaways to shrink into the smallest sloth of all. For a decade the species was reported as “fewer than 100”, from surveys that counted the mangroves, which cover under 3% of the island. The 2022 assessment, looking at the whole island, puts the population at 2,000–2,500 — better news that is still a rounding error of a species, Critically Endangered at every assessment since 2006, with visiting timber harvest and tourism pressure on its only home.

A pygmy three-toed sloth among leaves on Isla Escudo de Veraguas, Panama — the only license-safe photograph of the species — **The whole species lives here.** A pygmy sloth on Isla Escudo de Veraguas — as far as we can find, the only license-safe photograph of the species in existence, which says something about how rarely anyone reaches it. Photo: Lider Sucre, CC BY-SA 3.0, via Wikimedia Commons

A wild maned sloth at night, fur wet, in a tree in Brazil's Atlantic Forest — **Two species since 2022.** A maned sloth at night in Brazil's Atlantic Forest. In 2022, DNA split the maned sloth into northern and southern species — instantly turning one Vulnerable listing into two Endangered ones, each in a forest more than 80% of whose fragments are under ten hectares. Photo: ZOOVANCHO180, CC0, via Wikimedia Commons

The modern threat list

What actually kills a sloth in 2026

Gaps in the canopy. A sloth crosses a road the way you saw on page 3: slowly, on the ground, in the open. Fragmented forest forces those crossings constantly — the IUCN notes rising roadkill from Bolivia to the duplicated BR-101 highway through maned-sloth country.

Wires that look like branches. To a sloth, a power line is a vine with a grip problem. Costa Rica records thousands of wildlife electrocutions a year — the Sloth Conservation Foundation reports over half are sloths, and that only about a quarter of electrocuted animals survive. Dogs are the other ground-level hazard the forest never prepared them for.

Being adorable. The same face that made sloths famous feeds a trade: wild-caught animals — mostly infants pulled from their mothers — sold as pets or rented out as photo props. The one published study of the “sloth selfie” economy watched animals in Manaus and Iquitos being passed among an average of five tourists per session, handled by the head, limbs and claws. Every sloth researcher and rescue centre says the same thing: do not hold the sloth.

Checked — what gets repeated vs what was measured

Inflated“There are fewer than 100 pygmy sloths left”

Out of date, honestly earned. The famous count — 79 animals, 2012, PLoS ONE — surveyed the mangroves, which are less than 3% of the island. The 2022 IUCN assessment estimates 2,000–2,500 across the whole island. Still one of the smallest ranges of any mammal on Earth; still Critically Endangered.

Myth“Sloths make good pets and love being held”

Sloths are wild, solitary, and stress-concealing — stillness is their alarm response, which is exactly why they photograph so calmly. The selfie-trade study (Carder et al. 2018) and the IUCN assessments both treat handling and the pet trade as active threats to wild populations.

Contested“Most sloth species are fine”

Four of seven are Least Concern — and every one of the seven is assessed as decreasing, with no global population estimate for any species except the pygmy. “Fine” is doing a lot of work in that sentence.

Sources for this page

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