Eight orangutans have been released back into the wild in Borneo after they were taken into captivity when their habitat was threatened by wildfires over the summer.

Three mothers, their three daughters and two adult males were freed in a reserve in the west of the island on Friday, International Animal Rescue Indonesia (Yiari) and the forestry ministry said.

Indonesian authorities rescued 46 orangutans from fires in August and September. Wildfires in the region are usual for the country’s dry season but intensified this year.

The apes are critically endangered. Around 104,000 orangutans remain in Borneo and Sumatra, down from more than 230,000 a century ago, according to conservation group WWF.

While Indonesia is among many countries to grapple with wildfires each summer, this year’s were more intense due to the El Niño ocean warming phenomenon, which makes weather patterns more volatile and intense.

Yiari CEO Karmele Llano Sanchez said relocating the eight orangutans to the reserve was a “necessary step” when their habitats became unsafe.

Among them was Mama Nopi and her offspring Nopi, Naufal and Nopan, who had been surviving in a coconut and rubber plantation before their rescue in early September, Yiari said.

Fires had incinerated the surrounding forestry, restricting their access to food and bringing them closer to humans.