When It Gets Hot, Animals Lose Their Minds

A fish placed in front of a mirror sees its own reflection and attacks it. Strange behavior under any circumstances. At 84 degrees Fahrenheit (29 degrees Celsius), it turns out, it is simply what fish do.

A growing body of research shows that animals get their minds muddled during heat waves: birds struggle to learn, dogs bite more often, goat-like chamois pick fights over patches of food. The golden julie's mirror aggression is one data point among many in a field assembling a picture considerably stranger than it first appeared.

If animals can't stay alert enough to find food or avoid predators, their survival odds go downhill, says behavioral ecologist Amanda Ridley, who has spent years watching southern pied babblers in the Kalahari. In her experiments, birds needed twice as many trials during heat waves to learn a simple color-association task that cooler birds got quickly. The lesson was always the same; the heat made it unavailable.

The cognitive damage goes deeper than behavior. For insects and fish that cannot regulate their own body temperature, the problem is direct: a hotter environment means a hotter brain, which means impaired nerves, impaired memory, impaired judgment. Bumblebees taught to associate colors with food sources at 90 degrees Fahrenheit (32 degrees Celsius) failed the task at nearly twice the rate they did at 77 degrees (25 degrees Celsius). These are the pollinators that tomatoes depend on.

With heat waves growing more frequent, cognitive impairments across the animal kingdom could ripple through entire ecosystems. Chamois aggression on Italian mountain slopes is projected to rise 50 percent by 2080. If pollinators forget which flowers to visit, crops and wild plants follow.

Read the full story at Knowable Magazine, May 18, 2026

Hot Take: The fish attacking its own reflection was not having a bad day. It was having a warm one.