Three lions die of suspected heatstroke at Tokyo zoo as Japan swelters through 40°C heat
Three female lions at Tama Zoological Park died within a week, with autopsies pointing to dehydration and multiple organ failure. Ten of the zoo's 16 lions have fallen ill since mid-July as Japan endures another summer of punishing heat and high humidity.
Heat claims three lions in a week
The first signs appeared on 19 July, when Mugi, a three-year-old lioness, stopped eating. By the next day she could not stand. Zoo staff provided ventilation, water, subcutaneous fluids, liver tonics and vitamins, but she died on 28 July. Ichigo, an 11-year-old female, died on 31 July, and Luena, the oldest at 15, died on 2 August. Autopsies on all three showed systemic dehydration and multiple organ failure, pointing to heat stress as the cause. The zoo said final confirmation awaits laboratory results.
- Mugi, a 3-year-old lioness, loses appetite
- Mugi unable to stand; staff begin cooling measures
- Public access to lions suspended
- Mugi dies; autopsy shows dehydration and organ failure
- Ichigo, 11-year-old lioness, dies
- Luena, 15-year-old lioness, dies; three other lions remain seriously ill
Japan's relentless summer heat
The deaths come as Japan endures another summer of extreme temperatures. Some regions have hit 40°C in recent weeks, a threshold now labelled "cruelly hot days". Last year was the country's hottest summer on record, and this year's heat arrived suddenly after the rainy season ended in mid-July. The highest temperature ever recorded in Japan was 41.8°C, registered on 5 August 2025 in Isesaki. Between 20 and 26 July, nearly 18,600 people were hospitalised for heatstroke nationwide, and 45 were declared dead on arrival, according to the Fire and Disaster Management Agency. Japan records about 1,300 heat-related deaths annually and aims to halve that figure by 2030.
Why lions could not cope
Lions are considered heat-resistant, but the combination of high temperatures and extreme humidity proved fatal. Hideaki Karaki, professor of veterinary medicine at the University of Tokyo, explained that lions do not sweat; they pant to expel moisture from their airways, and evaporation cools the body. In high humidity, that mechanism fails. "The heat here comes with high humidity; that is different from the dry heat in Africa," a zoo spokesperson told AFP. Karaki added that the sudden temperature spike after the rainy season left the animals no time to acclimatise.
This is the first time we've experienced anything like this. Last year was also hot, but none of our lions fell ill like this.
Zoo scrambles to protect remaining lions
Tama Zoological Park, which has kept lions since 1964, houses 16 lions: five males and eleven females, aged one to twenty. Ten developed symptoms such as loss of appetite and reduced activity from mid-July, and public access was suspended on 23 July. Three lions, two males and one female, remain seriously ill and unable to stand; staff are administering intravenous fluids, medication and vitamins daily. Four others have recovered, and six were healthy throughout. The zoo is now installing portable air-conditioners and industrial fans in a private enclosure, watering facilities and improving ventilation. "Some of the lions are showing signs of improvement," Kosaka told the BBC.
A first in the zoo's history
The zoo had never recorded a heat-related lion death before. "Non si è mai verificato un caso di morte di leoni per caldo al Parco Zoologico Tama," a Tokyo metropolitan government official said. The incident has drawn widespread attention in Japanese media. Scientists note that human-caused climate change is increasing the frequency and intensity of extreme heat episodes in Japan and globally.
