One Island, One Sloth, Fewer Than a Hundred Left

Isla Escudo de Veraguas separated from mainland Panama around 9,000 years ago. The three-toed sloths stranded there shrank, as island mammals often do, and became Bradypus pygmaeus — about 40 percent smaller than their mainland relatives, and formally described only in 2001.

Their range is a fringe of red mangrove around an island of roughly 4.3 square kilometres. Surveys have repeatedly counted fewer than a hundred individuals. The IUCN lists the species as Critically Endangered, and the threats are mundane rather than exotic: mangrove cutting, disturbance from visiting fishers and tourists, and the simple fragility of a population that small.

Brazil's maned three-toed sloth is Vulnerable for a different reason. It is not confined to an island but to the shredded remains of the Atlantic Forest, and it depends on a narrow set of tree species. A forest fragment that lacks them is, from a maned sloth's point of view, not forest at all.

Slowness makes both cases harder. A sloth cannot outrun a chainsaw, cannot cross a road quickly, and cannot easily recolonise a patch once it is empty. Females typically produce one young a year, so recovery, when it happens, happens at sloth pace.

The interventions that work are unglamorous: keep the mangroves standing, keep canopy corridors connected across gaps, and give the animals time. Time is the one thing sloths have always been good at using.