When researchers Kim Lea Holzmann and Pedro Alonso-Alonso set off on a year-long expedition in the Amazon rainforest, they didn’t pack winter clothes. Who would? The Amazon is known for its warm, humid climate. But midway through the trip, in June 2023, they were in for a shock.
The temperature in southern Peru suddenly dropped from 23.9°C to just 10.5°C – and it stayed cold for nearly a week. But local researchers weren’t fazed – these cold snaps, usually caused by chilly air sweeping up from Antarctica, happen more often than outsiders realise (between 1980 and 2017, 67 cold spells were recorded in the area).
Holzmann and Alonso-Alonso, both PhD students at the University of Würzburg, saw this as a rare research opportunity. How does wildlife react to these unexpected periods of cold?
Until now, studies in the Amazon have focused on how cold spells affect agriculture. But this is the first time scientists have looked at their impact on wild animals.
Catching the cold wave
Using insect traps and camera traps already in place from previous studies, the team gathered data on insects and mammals before, during, and after the cold wave. What they found was both surprising and reassuring.
Insect activity dropped dramatically during the cold. Flying and ground-dwelling insects all but vanished – but most recovered fully within months.
One exception stood out: dung beetles. Their numbers stayed low, suggesting they’re more sensitive to the cold than other insect species.
How cold can insects go?
To understand more about the kind of temperatures the insects could handle, the team collected specimens from the rainforest and cooled them down in the lab.
Most coped well, but a quarter of the species studied entered a state of torpor – becoming immobile – at just a degree below the coldest temperature recorded in the forest.
If future cold spells grow harsher, these insects could be in trouble, say the researchers.
What about other animals?
Mammals were less active during the cold wave too, likely conserving energy by moving less. But like the insects, they bounced back after the cold passed.
"We didn't collect data on birds, reptiles and amphibians, but our subjective observations show that these animal groups were also less active than usual. During the cold wave, the rainforest was unusually quiet," says Holzmann.
The study, published in Biology Letters, highlights how even tropical wildlife must adapt to sudden cold snaps. And with climate change making weather more unpredictable, understanding these shifts is more important than ever.
Find out more about the study: Cold waves in the Amazon rainforest and their ecological impact
Main image: Amazon rainforest. Credit: Getty
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