The world's only known albino orangutan has arrived in a protected forest in Indonesian Borneo a year and a half after it was found malnourished in a cage, as seen in images published by epa-efe on Saturday.

The animal, named "Alba," arrived at a national park in Central Kalimantan province with "Kika" – another female orangutan – on Wednesday, according to Borneo Orangutan Survival Foundation (BOSF), which was in charge of its rehabilitation.

"Following a long and arduous 16-hour journey over land and by river, on Wednesday, 19 December, Alba and Kika finally arrived at the Bukit Baka Bukit Raya National Park (TNBBBR) to start the new chapter in their lives as true wild orangutans," the BOSF said in a press release on Saturday.

"Alba has consistently displayed sound climbing skills and moves with ease around the branches, which are good indicators that she may be ready to live in the wild," BOSF CEO Jamartin Sihite had said earlier.

The decision to return Alba to her natural habitat was backed by local authorities, as well as the government environmental conservation agency, BKSDA.

In April 2017, BOSF sheltered Alba at its rehabilitation center after she was rescued at around age five from the village of Tanggirang, where a local had caught her and held her captive.

The orangutan has been classified as a severely-threatened species by the International Union for Conservation of Nature.

The number of orangutans in Borneo dropped by 148,500 between 1999 and 2015 due to poaching and deforestation, according to a study published in February by the scientific journal Current Biology.