An endangered Borneo orangutan died Thursday at Indonesia's "death zoo", the latest in a series of suspicious animal deaths that have prompted calls to close the notorious facility.
Fifteen-year-old Betty the orangutan had difficulty breathing before she died, Surabaya Zoo spokesman Agus Supangkat said, adding she had just undergone a week of intensive treatment.
"Based on her medical records, she was suffering from inflammation of the lung," he said.
Supangkat said the inflammation was caused by "extreme hot weather that has hit Surabaya city".
The ape's death comes two weeks after a 12-year-old Borneo orangutan named Nanik died from an intestinal tumour and liver problems. Orangutans typically live between 50 and 60 years.
Supangkat denied any negligence by the zoo, saying the orangutans lived in a leafy outdoor enclosure and were given healthy diets of fruit, milk and multivitamins.
The Surabaya Zoo is Indonesia's largest and has been dubbed a "death zoo" as hundreds of animals have died prematurely or suffered abuse there in recent years.
In July last year a 15-year-old endangered orangutan at the zoo named Tori was forced to quit smoking. Management had allowed visitors to throw lit cigarettes at her for 10 years, making the smoking orangutan the zoo's star attraction.
Also last year a 30-year-old male giraffe died at the zoo with a 20-kilogram (44-pound) beachball-size lump of plastic in its stomach from food wrappers thrown into its pen by visitors.
Animal welfare groups have called for the zoo to be closed down, with British singer and animal rights activist Morrissey joining the chorus of criticism last year.
There are an estimated 45,000 to 69,000 Borneo orangutans left in the wild. They are native to the vast island of Borneo, shared among Indonesia, Malaysia and Brunei.
Destruction of Indonesia's lowland rainforest and peatland for palm oil plantations and agriculture has led to a dramatic decline in the number of orangutans, Asia's only great ape.
Explore further: The influence of the Isthmus of Panama in the evolution of freshwater shrimps in America