High temperatures compromise brain functions and increase aggression in animals, study reveals
Increasing heat waves, driven by rising global temperatures, may be affecting far more than just the physical well-being of animals. Recent findings, compiled in an analysis by Scientific American, based on diverse research, indicate that intense heat impairs fundamental brain faculties, hindering learning, decreasing the ability to react to dangers and even intensifying the frequency of aggressive behaviors in several species.
Impacts have been observed on a wide range of living beings, including birds, fish, mammals and insects. An experiment conducted in South Africa, for example, revealed that female southern white-winged robins performed worse on simple problem-solving challenges during warmer periods. While in mild temperatures they quickly learned to get around obstacles to obtain food, on days of intense heat, they repeatedly insisted on the wrong approach.
Other experiments demonstrate that these same birds needed twice as many attempts to correctly associate a specific lid with a food reward during heat waves. Similar patterns were identified in investigations with Australian zebra finches, which had difficulty finding a simple way out to obtain larvae, and with male guppies, which began to fail in maze courses, even when the reward was reproduction.
According to the researchers involved in this work, cognitive deterioration can represent a direct threat to the survival of the species. Animals that take longer to find food, fail to identify predators or lose the ability to acquire new strategies become more vulnerable in environments that are already under pressure from climate change.
Aggressive behavior and growing risks to ecosystems
Research also shows that heat can encourage more aggressive behavior. A study published in 2023, which analyzed almost 70,000 records of dog bites in eight cities in the United States, concluded that attacks were more frequent on hot, sunny days. The authors, however, emphasize that it is not yet possible to determine whether this change is restricted to animals or whether human heat stress also contributes to the increase in incidents.
A similar phenomenon has been recorded in other species. Chamois found in the Italian Apennines began to compete for food more intensely when temperatures rose and vegetation became scarcer. Small tropical fish, such as golden julies, demonstrated more aggressive reactions to seeing their own reflection when kept in heated water.
Pollinating insects can also suffer significant consequences. In tests carried out in Sweden, most bumblebees were able to learn to associate specific colors with food rewards when the temperature was 25°C. However, at 32°C, less than half achieved the same performance, which raises concerns about potential impacts on the pollination of agricultural crops and native plants.
Another relevant observation is the reduction in vigilance against predators. In experiments in the Kalahari Desert, birds exposed to temperatures close to 35.5°C lost the ability to distinguish a stuffed carnivore from a harmless object of similar size, reacting almost identically to both situations.
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Scientists consider that this type of behavioral modification can reduce the chances of survival in natural habitats, especially since several species depend on quick decisions to escape attacks or to locate limited resources.
Although the exact mechanisms vary between different groups of animals, researchers indicate that brain heating can compromise the functioning of nerve cells, directly affecting memory, learning and perception. The problem tends to be even more serious in species that cannot regulate their own body temperature, such as fish and insects.
The effects could become even more pronounced as extreme weather events become more frequent and longer-lasting. Regions such as the Kalahari Desert and tropical rivers are already experiencing accelerated warming, while urban areas often record temperatures higher than their surroundings due to the heat island phenomenon.
For the study authors, understanding how heat impacts animal cognition will be crucial to predicting the effects of climate change on entire ecosystems. If pollinators fail to find flowers, birds have difficulty nurturing their young, or prey fail to recognize predators effectively, the repercussions can reach far beyond a single species.
The researchers’ conclusion is that the impacts of extreme heat on the brains of animals are still little appreciated and may represent one of the least evident — but potentially most crucial — challenges for the adaptation of fauna on a warming planet.
