NTCO / Getty ImagesPoor ability to regulate body temperature makes sloths especially vulnerable during hotter periodsNTCO / Getty Images
Fish, tucuxi (Sotalia fluviatilis), and river dolphins (Inia geoffrensis) were not the only animals left dead on the riverbanks of the Amazon as a result of the heatwaves and extreme droughts of late 2023 and early 2024. From October to December 2023, biologists from Brazil’s National Institute of Amazonian Research (INPA) and the Federal University of Amazonas (UFAM) found 19 dead animals in a forest fragment near Manaus. The area has been monitored since 1998 and such a high number of deaths has never before been observed in just three months. Among the dead were ten brown-throated sloths (Bradypus variegatus), four agoutis (Dasyprocta sp.), two boa constrictors (Boa constrictor), two toucans (Pteroglossus sp.), and one silky anteater (Cyclopes sp.). The high mortality rate among sloths stems from their slow movement, which makes it difficult for them to move to cooler places, and their poor capacity to regulate body temperature, which is higher than the surrounding environment. Mortality was estimated at 1.3 sloths per hectare (ha)—more than half the density of living animals recorded in the same area, at 2.2 individuals per ha. Similar episodes are likely to recur, since heatwaves are becoming more intense and frequent (Acta Amazonica, June 9).
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