Massive forest fires in Indonesia that have caused a toxic haze to spread as far as Singapore and peninsular Malaysia are also seriously affecting endangered orangutans and their habitat, a rescue foundation said Tuesday.
Jakarta has deployed thousands of troops as temporary fireman and deployed dozens of water-bombing aircraft to battle blazes that are turning pristine forest into charred landscape in Sumatra and Borneo islands.
The fires -- usually started by illegal burning to clear land for farming -- have unleashed a choking haze across parts of southeast Asia.
The Borneo Orangutan Survival Foundation said Tuesday that the haze was affecting hundreds of great apes in its care at rescue centres and wildlife re-introduction shelters.
"The thick smoke does not only endanger the health of our staff... but also it affects the 355 orangutans we currently care for", the foundation said in a statement, referring to just once cetre in Kalimantan
"As many as 37 young orangutans are suspected to have contracted a mild respiratory infection," it added.
Conditions were so bad at their Samboja Lestari facility in East Kalimantan that outdoor activities for the animals had been restricted to a few hours a day.
Orangutans have been particularly vulnerable to commercial land clearances and have seen their natural habitat shrink dramatically in the last few decades.
The population of orangutan in Borneo has plummeted from about 288,500 in 1973 to about 100,000 today, according to the International Union for Conservation of Nature.
The toxic smoke caused by the forest fires is an annual problem for Indonesia and its neighbours, but has been worsened this year by particularly dry weather.
On Borneo island, which Indonesia shares with Malaysia and Brunei, pollution levels were "hazardous", according to environment ministry data.
Hundreds of schools across Indonesia and Malaysia were shut.