In Tecolutilla, Mexico, residents heard the thuds of howler monkeys falling from trees as temperatures soared past 43°C last spring. Overcome by dehydration and exhaustion, at least 83 primates were found dead in the state of Tabasco, with local vets estimating hundreds more perished across the region.
Such episodes are becoming more common as the climate crisis intensifies heatwaves. Flying foxes have tumbled from trees in Australia, billions of barnacles have baked in tide pools in Canada, and male beetles have been virtually sterilised by soaring temperatures. Scientists warn that extreme heat is driving species towards extinction faster than previously understood.
Maximilian Kotz, a climate scientist at the Potsdam Institute for Climate Impact Research, explains that rising average temperatures lead to a sharp increase in very hot days. While gradual warming has long been expected to push species out of habitats, heatwaves pose a unique threat, causing long-term population crashes that rival deforestation and habitat loss as drivers of biodiversity decline.
Kotz and colleagues analysed 70 years of data on over 3,000 bird populations and found that extreme heat had slashed tropical bird numbers by 25–38%. Tropical songbirds were hit hardest, as they already live near their heat tolerance limit and now experience dangerously hot days about ten times more often than in the past. The study suggests climate change has played a greater role in tropical bird declines than direct human activities like logging or farming.
During a 2021 heat dome in the Pacific north-west, air temperatures above 46°C killed an estimated 10 billion barnacles and 3 billion mussels in the Strait of Georgia alone, according to Prof Christopher Harley of the University of British Columbia. Attached to rocks, these creatures could not escape to cooler waters, highlighting the vulnerability of immobile marine life to extreme heat events.
