Cold shocks in the Amazon: How do wild animals respond?

A new study has revealed how sudden cold waves impact insects and mammals in the Amazon rainforest. 

Researchers from the University of Würzburg documented a rare cold spell in June 2023, during which temperatures plummeted from an average of 23.9°C to just 10.5°C. 

“Climatic conditions in tropical lowland rainforests are generally considered to be constantly warm and organisms are adapted to little fluctuations in temperature,” noted the researchers.

“However, even rainforests deep in the Amazon can be affected by cold waves.”

The team conducted the first comprehensive study on how wild animal communities in the Amazon lowlands respond to drastic temperature shifts.

Unexpected cold in the Amazon 

Local field assistants informed the research team that cold spells lasting several days are not uncommon in the Amazon. 

In fact, a similar but milder drop to 18°C occurred in 2022. However, the researchers were surprised by the severity and duration of the 2023 event. Recognizing the opportunity, they set out to study its effects on local wildlife.

Until now, studies on cold waves in the Amazon had largely focused on agricultural impacts. 

This study marks the first investigation into how these temperature fluctuations affect native insect and mammal populations, shedding light on how tropical species might cope with future climate variations.

How wildlife responded to the cold

The researchers analyzed biodiversity data collected in 2022, comparing it with data gathered during and after the cold spell. Their study included insect monitoring using traps to measure biomass of flying and ground-dwelling species.

The team also used camera traps to observe the behavior of large mammals, including jaguars, tapirs, and peccaries.

During cold tolerance experiments, insects were gradually cooled in a thermostat to determine their survival thresholds.

Insects show resilience, with one exception

During the cold wave, insect biomass and activity declined sharply, but most species fully recovered in the following months. 

The exception was dung beetles, whose populations remained lower even after temperatures returned to normal, suggesting they are more sensitive to cold than other insects.

Cold tolerance tests revealed that while most insects could survive temperatures lower than 10.5°C, about 25% were already near their physiological limits. 

These insects lost mobility at just 0.62°C below the recorded cold wave temperatures, meaning even slightly colder events could significantly impact their survival.

Mammals reduced activity to conserve energy

Unlike insects, mammals can regulate their body temperature. However, camera traps revealed a noticeable drop in their activity during the cold spell. 

The researchers believe this was a strategy to conserve energy, as maintaining body heat in colder conditions requires greater metabolic effort.

Once temperatures returned to normal, mammal activity levels rebounded. Though the study did not include birds, reptiles, or amphibians, researchers noted subjectively that these groups also appeared less active, contributing to an unusually quiet rainforest.

Cold waves in the Amazon

The study highlights that cold waves – defined as three or more consecutive days of significantly lower temperatures – are a recurring phenomenon in the Amazon. 

Between 1980 and 2017, 67 such events were recorded, some lasting up to eight days. These cold spells are typically caused by Antarctic air masses traveling north along the Andes and Brazilian highlands.

With climate change influencing global weather patterns, researchers speculate that these events may become more intense. If temperatures continue to drop beyond the tolerance of certain species, long-term ecological consequences could emerge.

Future research and conservation efforts

The study, part of the ANDIV project (Patterns and Drivers of Insect Diversity and Their Microbiome Along a Complete Forest Elevational Gradient in the Peruvian Andes), highlights the need for further research into how climate variability impacts Amazonian ecosystems. 

Supported by the German Research Foundation (DFG) and involving scientists from the University of Jena and LMU Munich, this ongoing project aims to understand how insect biodiversity is shaped by environmental changes.

As global temperatures fluctuate, understanding the resilience of Amazonian wildlife to unexpected cold spells will be crucial for predicting how climate change might reshape one of the world’s most diverse ecosystems.

The study is published in the journal Biology Letters.

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