With Justin Bieber, Rihanna and Katy Perry on heavy rotation, there seems at first little to distinguish Indonesia's Radio Kalaweit from any other pop station.

But in the breaks between the teen ballads and angst-rock from the likes of Linkin Park come darker messages that subvert those first impressions, bringing the issue of animal rights squarely into focus.

In one message sounds of gunfire are punctuated by gibbon cries and a voice that says darkly: "For one baby, five gibbons are killed."

"God did not create wild animals to serve as garden decorations," insists another jingle, between a piece of K-pop and the latest David Guetta tune.

"We know that if we just preached directly about animal rights, listeners would flee," said Aurelien Brule, a French national who founded Radio Kalaweit in 2003 and now goes by the name of "Chanee" -- gibbon in Thai.

Since he was 18 Chanee, now 32, has lived in Kalimantan, the Indonesian part of Borneo, where he has worked to protect endangered gibbons whose ranks have been decimated by rampant deforestation.

He said he fell in love with the primates after seeing them in a zoo as a child and was moved by their sadness at being separated from parents or partners.

"I wondered how we could get our message across to young people," said Chanee.

The idea behind the station was to use entertainment to educate and raise awareness of animal issues without beating listeners over the head about the plight of endangered species, he said.

It has paid off, with ratings surging. "Since 2003, we have been number one," said Willius Tinus, musical director and station organiser.

"Music is as important as the message. If you create a radio station that only talks about the environment, we know we will have no listeners," he said. Now many gibbons are discovered after tip-offs from listeners. Rescued primates are housed in a sanctuary, where Chanee and his team attempt to pair them up.

Gibbons cannot be returned alone to the wild because they would be killed by pairs protecting their own territory. But rampant deforestation has wiped out "empty" forest sites suitable for single gibbons.

Large tracts of Indonesia's jungle have been cleared for palm oil plantations due to surging global demand, one of the main reasons Indonesia is the third biggest emitter of greenhouse gases behind the US and China.

Indonesia has implemented a two-year moratorium on issuing new logging concessions on peatland and in other high-conservation forests. But unsustainable logging continues within companies' existing concessions.

-- Naming and shaming --

Awareness is not all the radio station strives for. Kalaweit -- meaning "gibbon" in the local dialect -- is also about what it sees as justice in shaming those who disregard laws against keeping gibbons as pets.

"We broadcast the names of anyone found to be holding a gibbon in a cage, even if it turns out to (be someone) as high ranking as the police chief or governor. Most times you get the animal two to three months later", Chanee explained.

The "kalaweit" sanctuary is home to more than 130 gibbons and also other animals including birds and crocodiles.

More than 60 percent of the animals who have been freed and now live there came as a result of "people who listened to the radio", Chanee said.

But to publicly pillory powerful Indonesian bureaucrats carries high risks. In 2006, police raided the station's office in a modest neighbourhood of Palangkaraya, the capital of Central Kalimantan province.

"They wanted to confiscate the transmitter," recalled Chanee. "But the DJs locked themselves in the building and they broadcast the raid on air. Five, then 10, and then 15 villagers arrived and the situation was defused."

As he speaks, French-Indonesian singer Anggun, who recently represented France at this year's Eurovision Song Contest in Azerbaijan, can be heard imploring on the airwaves: "Gibbons are not pets."

With the help of what he calls "sexy packaging", Chanee said Radio Kalaweit targets the 15-22 age group -- "an age when it is not yet too late to change attitudes".

Broadcasting over the Palangkaraya area, the station's audience varies "from 10,000-15,000 listeners a day" and commercial advertising ensures it is self-financing, according to Chanee.

"Kalaweit? It's cool," said Rabyatul Adawiyah who goes by the name "Zebi", a 17-year-old schoolgirl who comes from time to time after school to do some volunteer work in the tiny, barely air-conditioned station.

"Many people at school listen to it," she said, adding: "Even if it's the music that gets your attention, the environmental message is not far behind."