For animals such as fish and insects that can’t control their body temperature, heat waves could be particularly detrimental. “Changes in air temperature will affect brain temperature,” says Baird. A hotter brain could hinder the functioning of nerves, and that, she says, “might affect sensing, memory, and learning.”

Cross section shows band of cells in the mouse hippocampus.

Credit:
RAUNAK BASU / UNIVERSITY OF UTAH, SALT LAKE CITY

When Baird and colleagues tried to teach bumblebees to associate sweet sucrose with the color blue and bitter quinine with yellow, most of the bumblebees learned the trick at 77°, but fewer than half managed to do so at 90°. 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 pollinators suffer, but human agriculture too, Baird says.

Heat appears to dangerously diminish animal vigilance as well. In Ridley’s recent experiments, once mercury in the Kalahari Desert reached 96° F, pied babblers lost their ability to properly respond to predators. 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—they’d 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.

These studies are not just abstractions. In the Kalahari, where southern pied babblers use their wits to search for worms, temperatures are rising twice as fast as the global average. In tropical rivers, where male guppies seek mates, heat waves are growing longer and more intense. It’s the same story across much of the planet—temperatures climb, and animal thinking becomes strained, potentially putting species at risk. The effects may be magnified in certain areas such as cities, which often exhibit even warmer temperatures than non-urban areas. If anything, Ridley says, “We are probably underestimating the impacts of increased heat on animal minds.”

This story originally appeared on Knowable Magazine.