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A rare cold snap in the Amazon has plunged temperatures, prompting researchers to study the impact on wildlife. While most animals have adapted, some insects have shown vulnerability, raising concerns about future climate change.
Researchers working in the rainforest usually don't bring winter jackets and warm socks. After all, the region is known for its consistently warm climate. However, Kim Lea Holzmann and Pedro Alonso-Alonso have seen for themselves that this is not always the case. Both scientists, who are doing their doctoral theses at the Biocenter of the University of Würzburg, spent almost the entire year of 2023 in the Amazon region of southern Peru, studying biodiversity. On June 13, an unexpected cold snap dropped the temperature from an average of 23,9°C to 10,5°C. The cold spell lasted for almost a week.
“A year ago we already had a day when the temperature was only 18°C,” says Kim Lea Holzmann. But such a strong and prolonged cold snap seemed unusual to them. The local field assistants, however, were not surprised. They explained to the team from Würzburg that several days of cold snaps in the Amazon are not that rare.
First study of cold waves and wildlife
The research team decided to take advantage of the opportunity: how would wild animals react to a sharp cooling? "Until now, there have only been studies on the impact of cold waves on agriculture in the Amazon. We have presented the first-ever study of their impact on wildlife populations in the Amazon lowlands," Holzmann said. The results were published in the journal BiologyLetters.
Mammals in the Peruvian tropical forest
The researchers from Würzburg recorded these mammals in the southern Peruvian rainforest using camera traps: jaguar, pacu, agouti and peccary. Overall, the insects and mammals studied survived the cold wave well – with the exception of a few insect species. A third of the insects studied barely survived the measured low temperatures. Some species could face problems if such cold waves become even stronger in the future, which is quite possible given climate change.
Focus on insects and mammals
For the study, the team used data collected back in 2022 as part of a biodiversity study. The biomass of flying and ground insects was recorded using various traps. In addition, 12 camera traps documented the activity of jaguars, tapirs, peccaries and other mammals. The researchers re-collected this data during the cold wave and a few months after it ended. During the cold snap, the biomass and activity of all insects decreased significantly. In the following months, the situation fully recovered, except for a group of dung beetles, whose biomass remained low. They are apparently more sensitive to cold than other insects.
Insect vulnerability to cold
The researchers tested the cold tolerance of various insects by cooling them in a thermostat until they lost their mobility. It turned out that most insects can withstand even lower temperatures than those observed in June 2023. However, 25% of the insects studied fell into torpor at a temperature of just 0,62°C below the minimum temperature of 10,5°C. Torpor insects are completely immobile - if this state lasts for a long time, this can negatively affect their ability to survive.
Cold weather causes unusual silence in rainforest
Mammals were also less likely to appear in front of the cameras during cold weather. Unlike insects, they can maintain a constant body temperature. "To do this, they need more energy during the cold period, which they probably conserve by reducing physical activity," Holzmann noted.
Cold-sensitive beetles and spiders
Among the typical inhabitants of the lowland Amazon rainforest: the dung beetle Coprophanaeus lancifer, which was found to be sensitive to low temperatures, and the Brazilian wandering spider Phoneutria boliviensis, which is usually active at night, but was not seen during the cold snap. After the cold snap, mammals returned to their usual lifestyle. "We did not collect data on birds, reptiles and amphibians, but our subjective observations show that these groups of animals were also less active than usual. During the cold snap, the rainforest was unusually quiet."
Cold waves in the Amazon: natural phenomenon or climate trend?
Cold waves, in which temperatures drop sharply for at least three days, are common in the Amazon. Between 1980 and 2017, 67 such episodes were recorded there, some lasting up to eight days. A clear cycle of their occurrence has not yet been established. In most cases, cold waves are caused by air masses moving north from Antarctica along the Andes and the Brazilian plateau.
Research links
Cold waves in the Amazon rainforest and their ecological impact – Kim L. Holzmann, Pedro Alonso-Alonso, Yenny Correa-Carmona, Andrea Pinos, Felipe Yon, Gunnar Brehm, Alexander Keller, Ingolf Steffan-Dewenter, Marcell K. Peters. BiologyLetters, January 1, 2025.
Insect biodiversity in the Peruvian Andes
Kim Lea Holzmann and Pedro Alonso-Alonso from the Biocenter of the University of Würzburg are working on their doctoral research within the ANDIV project (Patterns and drivers of insect diversity and their microbiome along a complete forest elevational gradient in the Peruvian Andes) led by Dr. Marcel Peters and Professor Ingolf Steffan-Deventer. The project is funded by the German Research Foundation (DFG) with the participation of researchers from the University of Jena and LMU Munich.
