A wild mother and baby orangutan in West Kalimantan, Indonesia. Photo: Timothy Laman, National Geographic Image Collection

If there is paradise for monkeys, it might well be in Indonesia's East Kalimantan province, on the island of Borneo. Located in Southeast Asia, the island is home to the pig-tailed macaque, the grizzled leaf monkey and several other species. The king of the Borneo rainforest, however, is an ape -- the orangutan.

And a Nature Conservancy field scientist has just returned from Borneo with rare good news about the great ape: His team has found a previously undiscovered population living in East Kalimantan. For National Geographic Radio Expeditions, NPR's Christopher Joyce reports.

The orangutan doesn't look like other great apes. It has long, shaggy red hair and an oval face with deep-set eyes that look almost like the button eyes on a stuffed animal. The male is as big as a man and calls out from a nest high in the trees.

But to find an orangutan in the towering rainforest of Kalimantan, scientist Scott Stanley has to use his ears.

Scott Stanley, a Nature Conservacy field scientist in East Kalimantan, on Borneo. Photo: The Nature Conservancy

"You walk through the woods and you're going to hear gibbons," he tells Joyce. "You're going to hear other calls. You're going to hear hornbills. Helmeted hornbills or rhinoceros hornbills -- and then if you're really fortunate you can hear an orangutan long call, which is amazing, too, in itself."

Stanley says the call is basically a very low and long, drawn-out grunt. He compares it to the sound a human would make if he stepped on a tack.

The Nature Conservancy is conducting a survey to find out how many orangutans are left. In the wild, the apes live only on Borneo and the Indonesian island of Sumatra. Only about 20,000 may be left, and they could become extinct within the next few decades.

East Kalimantan is really a last refuge for a sizeable, viable population of orangutans, says Stanley. His team has so far surveyed a 300,000-acre area, looking for their nests in trees. Orangutans are the only great apes that live most of their life in trees, and they typically build a nest every night to sleep in.

Recently, Stanley surveyed a remote part of East Kalimantan called Berau. It's several days travel by canoe and by foot through dense, muddy forest. Stanley and his team were amazed by what they found there -- hundreds of orangutan nests. He calculated that as many as 2,000 orangutans lived there, close together, perhaps six animals in a square mile. And it was an undiscovered place -- an orangutan Atlantis.

In the wild, orangutans live only on the islands of Borneo and Sumatra. Click on map to see area detail. Graphic: Katherine Parker, NPR Online

"We were frankly surprised," says Stanley. "We had no idea that they would be at this level, at this density."

Stanley says this could be the biggest population of orangutans on the island, and it means an increase by 10 percent in the world's orangutan population. That's a big boost for conservation of the endangered animal.

But Kalimantan's human population is growing, and orangutans are losing out.

"They are so cute that people like to keep them as pets," says Ramon Janis, who works for the East Kalimantan provincial government. "And because of that there's an economic value to it. There's poaching of orangutans to be sold at the market or exported to some countries as pets. On the other hand, the orangutan is also a source of energy, of protein."

The biggest pressure is on the forests where the orangutans live. Timber companies are logging Borneo at a frantic rate. Indonesia depends on timber income as it struggles out of an economic depression. If too many trees are cut, the forest floor dries out.

Doug Fuller, a geographer at George Washington University in Washington, D.C., maps forests for the Indonesian government.

"As the selective logging continues," he says, "that makes the forest more and more susceptible to fire, and the sad thing is that many people are resigned to the fact now that Borneo is going to lose all of its forest cover in the next decade or so."

To that end, the Nature Conservancy has signed a deal with the hardware retailer The Home Depot. The company says it will buy Indonesian timber products from forests where logging leaves enough trees behind for wildlife, and will give the Conservancy $1 million to help certify the timber.