Three female lions at Tokyo’s Tama Zoological Park have died after weeks of extreme heat, with zoo staff attributing the fatalities to heat-related illnesses. The lions, named Mugi, Ichigo, and Ruena, died over a five-day period between July 28 and August 2, following a month marked by soaring temperatures and high humidity across Japan.
The zoo announced the deaths on Monday, stating that while the exact cause remains undetermined, initial postmortem examinations pointed to systemic dehydration and multiple organ failure. The facility indicated that heat stress was likely a contributing factor in the lions’ decline.
During July, Tokyo experienced an average heat index—reflecting combined temperature and humidity—exceeding 110 degrees Fahrenheit. Health officials in Japan designated July 23 as a “kokushobi,” or “cruel heat day,” underscoring the severity of the conditions.
Signs of heat-related illness appeared in the lions by mid-July, manifesting as loss of appetite and decreased activity. By July 22, 10 of the zoo's 16 lions displayed symptoms severe enough to require medical treatment. Zookeepers attempted to mitigate the effects by spraying the animals with water and administering intravenous fluids, but three lions ultimately succumbed.
The zoo also reported that while four of the affected lions have begun recovering, three remain critically ill and unable to stand. Care efforts continue with intravenous fluids, liver tonics, vitamins, and treatment for pressure sores.
Experts note that lions are more adapted to dry heat environments, and high humidity hampers their natural cooling mechanisms, such as panting and seeking shade. Aaron Whitnall, a zookeeper in England who cares for multiple lions, emphasized the importance of enhanced cooling measures—including shade provision, cooling pads, and misting—when temperatures and humidity become excessive. He also described innovative heat-mitigation techniques used at his own sanctuary, including frozen animal blood shaped into ice pops to keep big cats hydrated and cool.
Similar measures have been adopted by zoos worldwide facing heat stress. The Smithsonian National Zoological Park in Washington, D.C., for example, provides frozen meat blocks for carnivores and frozen fruit snacks for herbivores when heat indices surpass 90 degrees Fahrenheit.
Across Japan, various zoos have implemented steps to protect their animals amid the heatwave. Inokashira Park Zoo in Tokyo suspended outdoor guinea pig interaction programs due to high temperatures. Ueno Zoo has installed pools, fans, and misting systems to cool its animals, sharing images of penguins cooling off under sprayed water. Farther north, Asahiyama Zoo in Hokkaido has distributed ice blocks infused with honey and fruit to pandas and macaque monkeys.
Tama Zoological Park has closed its lion enclosure to the public since July 23 and announced that it will remain closed until further notice as the facility continues to manage the health challenges posed by the prolonged heat.