It’s not always warm and pleasant in the Amazon rainforest; cold waves can lead to significant drops in temperature. Researchers have explored how animals adapt to these conditions.
Typically, individuals conducting research in tropical rainforests wouldn’t think to pack warm clothes like winter jackets and socks. This region is often associated with consistent warmth. However, Kim Lea Holzmann and Pedro Alonso-Alonso learned otherwise during their time in the Amazon. Both are pursuing their doctoral theses at the Biocentre of the University of Würzburg and spent nearly all of 2023 studying biodiversity in southern Peru.
On June 13, a cold spell hit the region, causing temperatures to drop dramatically from an average of 23.9 to 10.5 degrees Celsius. This chilly weather lasted for almost a week. “The previous year, we encountered a day with temperatures as low as 18 degrees,” recalls Kim Lea Holzmann. However, such an extreme and extended cold was surprising to them. Meanwhile, local field assistants were not as taken aback, explaining to the Würzburg team that multi-day cold snaps are not uncommon in the Amazon.
First Study on Cold Waves and Wildlife
In response to these weather changes, the research team decided to investigate how wildlife reacts to cold spells. “Previous research only focused on the impacts of cold waves on agriculture in the Amazon. We’re presenting the first study examining their effects on wild animal communities in this part of the Amazon,” states the doctoral student. Their findings have been published in the journal Biology Letters.
The results indicate that, overall, the insects and mammals observed managed quite well during the cold wave, except for some insects. Additionally, the cold tolerance of a quarter of the insects studied was nearly reached due to the low temperatures recorded. Certain species might struggle if future cold waves become harsher, a possibility considering climate change.
Focus on Insects and Mammals
For this study, the research team utilized data collected in 2022 during their biodiversity assessment. They measured the biomass of flying and ground-dwelling insects using several insect traps and documented the activity of jaguars, tapirs, peccaries, and other mammals with twelve camera traps. This data was collected again during the cold spell and a few months after it ended.
Throughout the cold wave, there was a noticeable decrease in the biomass and activity of all insect groups. Yet, they showed complete recovery in the subsequent months, except for dung beetles, which appeared more sensitive to the cold compared to other insects.
The researchers assessed the cold tolerance of various insects by gradually cooling them in a thermostat until they became immobile. Most insects showcased the ability to endure temperatures lower than those experienced during the June cold snap. However, 25% of the insects were found to enter a state of torpor when temperatures dipped just 0.62 degrees Celsius below the measured 10.5 degrees. “In this immobile state, lasting longer can negatively affect their survival,” explains Pedro Alonso-Alonso.
Cold Caused Unusual Calm in the Rainforest
Similarly, the mammals monitored appeared less frequently in front of camera traps during the cold spell. Unlike insects, mammals regulate their body temperature. “During the cold, they require more energy, which they likely conserve by lowering their activity,” notes Kim Lea Holzmann.
After the cold wave, the mammals resumed their regular behaviors. “We didn’t collect specific data on birds, reptiles, and amphibians, but our observations suggest that these groups were also less active. The rainforest was unusually quiet during the cold spell,” they added.
Insect Biodiversity in the Peruvian Andes
Kim Lea Holzmann and Pedro Alonso-Alonso are involved in the ANDIV project (Patterns and drivers of insect diversity and their microbiome along a complete forest elevation gradient in the Peruvian Andes) for their doctoral studies, supervised by Dr. Marcell Peters and Professor Ingolf Steffan-Dewenter. This project is funded by the German Research Foundation (DFG), alongside researchers from the University of Jena and LMU Munich.
Background: Cold Waves in the Amazon Rainforest
Cold waves that last for at least three consecutive days, causing sharp temperature drops, are relatively common in the Amazon Basin. Between 1980 and 2017, 67 such cold spells were recorded, some lasting up to eight days. Currently, no clear cycle for their occurrence has been established. Typically, these cold waves are attributed to frigid air fronts moving northward from Antarctica, traveling parallel to the Andes and Brazilian highlands.
