Three female lions have died from suspected heatstroke at Tama Zoological Park in Tokyo as Japan swelters in temperatures reaching 40°C.
Since mid-July, 10 of the 16 lions kept at the facility have suffered severe symptoms, including loss of appetite and decreased activity, during the punishing summer heatwave.
Zoo staff attempted to save the struggling animals using industrial fans, water sprays, and intravenous fluids, but three lionesses lost their lives. One lion died on Tuesday, another on Friday, and a third on Sunday.
Tama Zoological Park, located in Hino, Tokyo, is one of Japan's major wildlife facilities and features expansive naturalistic enclosures for big cats.
Autopsies performed on the lionesses revealed systemic dehydration and multiple organ failure in all three animals. A spokeswoman for the zoo confirmed that veterinary staff suspect heatstroke caused the deaths, though official confirmation awaits laboratory test results.
"According to our veterinarian, the cause of the deaths is suspected to be heatstroke as dehydration and multiple organ failure were observed," a spokeswoman said. "Even though lions are thought to be resistant to heat, zoo keepers have been strengthening countermeasures to cope with Japan's summer heat in recent years. Heat here comes with high humidity - that is different from heat with dry air in Africa."
The deceased lionesses were identified as 15-year-old Luena, 11-year-old Ichigo, and three-year-old Mugi. Mugi first showed a loss of appetite on July 19 and was unable to stand by July 20. Staff provided ventilation, water, subcutaneous fluids, liver tonics, and vitamins, but she died on July 28. Ichigo died on July 31, followed by Luena on Sunday.
On Monday, zoo officials reported that three other lions at the facility, two males and one female, remain unwell and unable to stand. Keepers are administering fluids, medication, and vitamins to assist their recovery.
Humidity and Heat Stress Factors
Animal welfare experts note that extreme humidity and enclosure restrictions played a major role alongside the 40°C temperatures. Samantha Ward, Professor of Zoo Animal Welfare and Legislation at Nottingham Trent University, explained that lions rely on specific behavioural and respiratory mechanisms to manage heat.
"Lions do not sweat effectively like humans," Professor Ward said. "They rely heavily on behavioural strategies, respiratory cooling (panting), shade-seeking and reducing activity. When humidity is high, evaporative cooling becomes less effective."
In the wild, lions remain inactive for much of the day, resting in shade and moving across vast areas to find cooler spots. Captive zoo animals have far fewer options to escape rising temperatures.
"It's also worth noting that these lions have never experienced 'the wild' and African temperatures, therefore although their physiology is built for heat, if the lions are not used to it, especially with rapid spikes in temperature this could also cause problems," Professor Ward added.
Welfare Warnings for UK Zoos
Professor Ward warned that climate change makes extreme heat a foreseeable welfare risk for zoos globally, comparing it to flooding or disease outbreaks. She cautioned that facilities in the UK could face a similar fate as temperatures once considered exceptional become more frequent.
"I do not think UK zoos should assume that traditionally 'warm-climate' species will automatically cope with British heatwaves," Professor Ward told the Daily Mail. She noted that UK facilities were historically designed around a temperate climate, focusing on preventing cold stress rather than managing extreme heat.
"UK zoos may face a particular challenge because many facilities were designed around a relatively temperate climate. Historically, far more attention was given to preventing cold stress than extreme heat," she explained.
Vulnerable species extend beyond lions. Professor Ward highlighted that older animals, large carnivores, species adapted to cooler climates, and animals with underlying health conditions face heightened heat risks.
Preventative Measures for Animal Care
To protect animals from severe heat stress, Professor Ward outlined key interventions that zoos should implement during extreme weather:
- Increased shaded areas throughout enclosures
- Additional indoor climate-controlled refuges
- Mist systems and water features where appropriate
- Improved ventilation in indoor housing
- Real-time temperature and humidity monitoring
- Heatwave action plans with defined intervention thresholds
- Behavioural monitoring to identify early signs of thermal stress
- Adjusting feeding and enrichment schedules to cooler periods
- Temporary access restrictions to public viewing areas if animals need protected cooling spaces
- Species- and individual-specific heat-risk assessments
Professor Ward added that closely monitoring changes in animal behaviour can provide vital early warnings before thermal stress becomes life-threatening.
Dr Paul Rose, from the Centre for Research in Animal Behaviour at Exeter University, offered an additional perspective. He stated he would be surprised if heatstroke occurred in a healthy adult lion in the UK, but warned that older individuals and cubs remain susceptible to heat exhaustion and stroke.
"Animals that live at good zoos in the UK will receive extra care in hot weather," Dr Rose said. "We are prepared for such scenarios in zoos and keepers work hard to ensure that animals are kept comfortable."
Rising Temperatures and Climate Trends
Scientists report that human-induced climate change is increasing the frequency and intensity of extreme heat events in Japan and worldwide.
Japan recorded its highest temperature on record on August 5, 2025, when mercury reached 41.8°C in Isesaki, located north of Tokyo.
The human toll of the extreme weather is also severe. Japan's Fire and Disaster Management Agency reported that close to 18,600 people were taken to hospital for heatstroke between July 20 and July 26, with 45 pronounced dead on arrival.
Following the tragedy, Tama Zoological Park announced it is introducing further measures to protect its lion pride, including increased water sprinkling, improved ventilation, and the installation of spot air conditioners.
