TOKYO(National Times)- Three lions at a Tokyo zoo have died from suspected heatstroke and others are under treatment, a spokeswoman said on Tuesday, with the big cats struggling with high humidity.

Japan sweltered through its hottest summer on record last year and parts of the country have hit 40C in recent weeks, qualifying for the new designation “cruelly hot day”, with thousands of people hospitalised.

Ten of the 16 lions in Tama Zoological Park have suffered symptoms such as “loss of appetite and decreased activity” since mid-July, and three lionesses died, the zoo said in a statement.

One three-year-old female died on Tuesday, another aged 11 died on Friday, and the third on Sunday aged 15. The Tama Zoological Park said the lion enclosure, where visitors can normally be driven around in zebra-pattern “safari” buses, was closed to the public until further notice.

“According to our veterinarian, the cause of the deaths is suspected to be heatstroke” because 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,” she said.

The spokeswoman said the heat “arrived suddenly” this summer after the rainy season ended in late July. “We are strengthening measures against the heat (further), sprinkling water, improving ventilation and installing spot air conditioners,” she said.

Several lions are still being treated, she added.

Animal rights group PETA said the lions named Mugi, Ichigo and Luena “were born, lived, and died in confinement, deprived of everything that makes life worth living for a wild animal”.

“Zoos are not rescues or sanctuaries; they exist to display animals for profit, not to put animals’ needs first,” PETA said in a statement.