A Sumatran rhinoceros is pregnant with her second calf at an Indonesian sanctuary in the original habitat of the highly endangered species, a government conservation official said Wednesday.

Bambang Dahono Adji, director of biodiversity conservation at Indonesia's Ministry of Environment and Forestry, said the mother, Ratu, is expected to give birth next May at the Way Kambas National Park in southern Sumatra, to join five other rhinos there.

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A Sumatran rhino roams at Gunung Leuser National Park in Aceh province, Indonesia. There are about 100 Sumatran rhinos left in the world, almost all of them in Indonesia. (Leuser International Foundation/Associated Press)

Sumatran rhino pregnancies last about 16 months and the babies weigh up to 27 kilograms. Ultrasound images indicate Ratu's pregnancy is progressing normally.

"This proves capabilities of our own experts at Way Kambas," Dahono said. "Malaysia's announcement of the extinction of Sumatran rhino there made Indonesia's efforts to save the rhino very important now."

Now 12 years old, Ratu was born in the wild and wandered out of the rainforest in 2005. Her first calf, a male named Andatu born in 2012, was the first Sumatran rhino born in an Asian breeding facility in more than 140 years.

Critical time

The father of both calves is Andalas, who was born at the Cincinnati Zoo, later sent to the Los Angeles Zoo, and then moved to Indonesia in 2007 for mating.

Andalas' brother, Harapan, lives at the Cincinnati Zoo, is the only Sumatran rhino abroad and is expected to be moved to Indonesia in October for mating. Their sister Suci was believed to have died there because her diet at the zoo contained too much iron.

Sumatran rhino 'video trapped'1:07

"We are proudly announcing the pregnancy of Ratu at the Sumatra Rhone Sanctuary coinciding with the celebration of World Rhino Day," Environment Minister Siti Nurbaya Bakar said in a statement. World Rhino Day was Tuesday.

She added that "the pregnancy represents decades of international collaboration to save this endangered species."

Susie Ellis, executive director of the International Rhino Foundation, noted that said the pregnancy comes at a critical time for the species, which has no more than 100 animals left in the wild.

"One birth doesn't save a species, but it's one more Sumatran rhino on Earth," said Ellis.

The species is seriously threatened by loss of habitat and poaching for their horns..