They call it stupid hot for a reason: Heat muddles animal brains
On a blazing hot day in South Africa, female southern pied babblers can鈥檛 think straight. The medium-sized black-and-white birds are trying to get at tasty mealworms behind a see-through barrier. On cooler days, the birds can quickly figure out that all they have to do is go around the small wall of plastic. But when the mercury goes up, the birds just keep stubbornly pecking at the barrier.
That experiment is part of a growing body of research showing that animals get their minds muddled during heat waves. When it鈥檚 hot outside, birds struggle to learn, dogs bite more often, goat-like chamois pick fights, reports. This is bad news not just for those who get on Fido鈥檚 toasted nerves. If the animals can鈥檛 stay alert enough to find food or avoid predators, their chances of survival go downhill, says , a behavioral ecologist at the University of Western Australia who coauthored the pied babbler study.
With climate change making heat waves more common, such cognitive impairments across the animal kingdom could ripple through entire ecosystems, putting already fragile species at greater risk. If pollinators forget which flowers to visit, crops and wild plants may fail. If birds can鈥檛 find food as easily, their young may not survive. And on a warming planet, a sharp mind is particularly vital. 鈥淎 changing climate means that your ability to behaviorally adapt is even more important,鈥 Ridley says.
Hotheaded
There is plenty of evidence that animals are affected by heat. Birds, for example, spend and ; they even . Instead, they鈥檒l sit around for hours with wings spread to dissipate the heat, and pant with their beaks wide open. Some animals retreat to shade or hide in cool burrows 鈥 again, skipping meals. Bees, meanwhile, splash their faces with droplets of water midflight when the weather is sizzling. This way, 鈥渢hey get convective cooling for their brain,鈥 says , a neuroscientist at Stockholm University.
Some of the first hints that hot temperatures can mess up minds, however, came from studies on humans. Back in the 1800s, Belgian astronomer Adolphe Quetelet noticed that violent crime in France . Later studies linked high temperatures with , mental-health-related , and . When it鈥檚 hot, people have trouble , and their. For students at schools without air conditioning, a school year just one degree Fahrenheit hotter by 1%, a study found.
Increasingly, there鈥檚 evidence that other species may also be more aggressive when mercury shoots up. A 2023 study that combed through nearly 70,000 reports of dogs biting people across eight U.S. cities, from Chicago to Baltimore, found that such incidents were more likely to happen on days. The risk was 10% higher on a 90-degree day than on a 60-degree day 鈥 and not only because people are more apt to venture out for walks when the sun is shining (the researchers controlled for seasonal effects in their data).
Still, the scientists were unable to determine whether dogs become more aggressive as it gets hot, or if cranky humans provoke more attacks. 鈥淚t鈥檚 likely that both humans and dogs get stressed and more irate at higher temperatures,鈥 said Clas Linnman, a neuroscientist at the University of Miami and a coauthor on the study.
And it鈥檚 not only dogs: A 2025 study out of China showed that many animals, including snakes and cats, are more inclined to bite people when it gets hot.
Animals also seem to lose their cool with each other, especially if there is food involved. Scientists used binoculars and spotting scopes to spy on that feed on protein-rich plants on the slopes of the Italian Apennine Mountains. More than 1,600 hours of observations over two summers revealed that when temperatures rose from 54 to 64 degrees Fahrenheit, vegetation grew scarcer, and . The animals became territorial over patches of food, they assumed threatening postures, chased each other 鈥 attacks that, at times, escalated. The study authors predict that chamois aggression will go up 50% by 2080 due to climate change.
The small tropical fish called Golden Julie also gets confrontational in the heat. Ordinarily, when a Golden Julie is placed in front of a mirror, it sees its reflected image as a stranger and shows some hostility, raising its fin, for example. But if the normally 78-degree water is raised to a hot 84 degrees, the fish is more likely to get aggressive, and may bite or slap its tail against the mirror, as it tries to scare or attack the reflected image.
Cognitive problems
Heat waves can also hamper the ability of animals to learn, as Ridley and her colleagues observed with the southern pied babblers. In one of their experiments, the birds were presented with a simple wooden block with two holes drilled in it, each covered with a lid. If the bird pecked at the lid, it would rotate, revealing either an empty hole or a tasty mealworm (the babblers, Ridley says, 鈥渁re highly motivated by mealworms鈥). One lid was dark, and the other a lighter shade of the same color. During heat waves, the birds needed twice as many trials to learn that the mealworm was always hidden under the lid of the same shade.
Another group of scientists , pretty Australian songbirds, and discovered that if temperatures are high, they too have cognitive problems. When figuring out how to get a mealworm out of a see-through tube with an opening at one end, they would just keep pecking on the tube, says study coauthor , an evolutionary biologist at the University of Tennessee, Knoxville. It鈥檚 the bird equivalent of 鈥渂anging your head against a brick wall,鈥 she says.
Adding to the tally, several years ago researchers showed that when the heat is on, finding their way around a maze and forget objects they鈥檝e seen the day before. More recently, researchers found that , popular aquarium fish, also have trouble getting through a maze after spending several days in heat-wave-like 90-degree water, even if the prize for getting it right is a virgin female, which they tend to find particularly attractive.
For animals such as fish and insects that can鈥檛 control their body temperature, heat waves could be particularly detrimental. 鈥淐hanges in air temperature will affect brain temperature,鈥 says Baird. A hotter brain could hinder the functioning of nerves, and that, she says, 鈥渕ight affect sensing, memory and learning.鈥
When Baird and colleagues and bitter quinine with yellow, most of the bumblebees learned the trick at 77 degrees, but fewer than half managed to do so at 90 degrees. Such impaired cognition could spell trouble in the field: If the insects forget which flowers they should pollinate (in the case of bumblebees, these include tomatoes and blueberries) or how to get back home with nectar, not only will the , but human agriculture too, Baird says.
Heat appears to dangerously diminish animal vigilance as well. In Ridley鈥檚 recent experiments, once mercury in the Kalahari Desert reached 96 degrees Fahrenheit, In their studies, researchers lured birds toward a mystery shape covered in a sandy-colored blanket, using worms as bait. Once a babbler approached, the scientists would reveal what was hidden underneath: either a taxidermied cat-like carnivore called a genet, or a similarly sized and colored wooden box. The birds got scared of the genet in cooler temperatures 鈥 they鈥檇 call out, scan their surroundings, or simply flee. But once it got hot, they behaved similarly whether they were facing the carnivore or the box. Ridley suggests that this could translate into higher chances of fatal predator attacks as heat rises, which could harm populations of babblers and other prey species.
Heat hampers brain cells
In addition to highlighting behavioral changes, animal studies can also offer insight into how heat meddles with brain cells. Experiments with mice, for example, show that in the hippocampus, the brain鈥檚 memory center, and can lead to the death of neurons there. If in early life, their adult brains have fewer mushroom bodies 鈥 structures that are important for insect learning. And a 2025 study on cleaner wrasses, a fish species that cleans parasites off other fish, showed that after a heat wave, a key part of the fish brain that controls cognitive functions such as memory .
These studies are not just abstractions. In the Kalahari, where southern pied babblers use their wits to search for worms, temperatures are rising as the global average. In tropical rivers, where male guppies seek mates, . It鈥檚 the same story across much of the planet 鈥 temperatures climb, and animal thinking becomes strained, potentially putting species at risk. The effects may be magnified in certain areas, , which often exhibit even warmer temperatures than non-urban areas. If anything, Ridley says, 鈥淲e are probably underestimating the impacts of increased heat on animal minds.鈥
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