The skull of a rare mountain gorilla that was killed is kept in a box at Virunga National Park in Rutshuru, Congo. In the world of wildlife conservation, the biggest worry most rangers face is preventing the extinction of endangered animals. But in Virunga National Park, where more than 120 rangers have been killed over the past decade, rangers worry, too, about their own survival.

Virunga National Park, Congo ? Not far from a hillside where several mountain gorillas shot dead last summer lie buried, park ranger Innocent Mburanumwe peers across a primordial canopy of treetops into what may be the most dangerous game reserve on earth.

The lush sanctuary – home to some of the world’s last mountain gorillas – was thrust onto the front lines of Congo’s latest war in September. Since then, the fragile habitat in the Central African highlands has been overrun by rebels and soldiers, transformed into an off-limits war zone.

In the world of wildlife conservation, the biggest worry most rangers face is the extinction of endangered animals. But in Virunga National Park, where more than 120 rangers have been killed over the past decade, they also worry about their own survival.

In recent months, some have dodged bullets while driving in their cars. Some have spent nights hiding under beds with their families. All were forced to flee the park’s so-called gorilla sector when rebels swept in, some taking shelter in tents on the sanctuary’s edge.

“There are undoubtedly risks associated with this job,” says Mburanumwe, 35, whose brother – also a ranger – was killed in the line of duty a decade ago. “But our concern is for the gorillas. That’s the reason we’re here.”

The gorillas have the potential to draw tourist revenue to a desperately poor region and bring in vital funding through conservation groups. Over the past 12 months, though, rangers have watched helplessly as the gorillas have been massacred.

2007 was the apes’ bloodiest year on record since famed American researcher Dian Fossey first began working in Congo in the mid-1960s to save them. The toll: 10 shot and killed, two others missing. The rangers don’t know for sure who killed the gorillas, but they believe illegal charcoal traders are trying to sabotage the park for easier access to its trees.

Now armed groups have seized the habitat. With park staff unable to set foot inside the reserve for the past four months, the gorillas’ fate is unknown.

“Nobody knows what’s happening to them, nobody can track them anymore,” Mburanumwe says bleakly, eyes fixed on the verdant slopes of dormant Mikeno volcano, where about 190 of the world’s remaining 700 mountain gorillas live.

“It’s a catastrophe,” he says, turning away from the mountain, its mighty peak rising through the mist. “For them and for us.”

120 rangers dead

The biggest threat are militias and rebels from Congo, Rwanda and Uganda. Some rangers have been abducted and forced to work as guides for armed groups unfamiliar with the terrain. Rwandan militiamen held ranger Anicet Baziheraho for three weeks last year until he escaped from their forest base. “They tied me up and beat me,” he says, showing scars on his wrists from the ropes. “They said I was a spy.”

In the past decade about 120 of the 660 rangers have been killed on the Congo side of the border alone, a tenth of them in the gorilla sector.

Meanwhile, the gorilla population in Central Africa’s Virunga Conservation Area – a fertile volcanic mountain chain spanning the frontiers of Congo, Rwanda and Uganda – has risen by roughly 10 percent over the same period to about 380 today. The world’s other 320 mountain gorillas live farther north in Uganda’s Bwindi Impenetrable Forest.

Six crosses

Beside the park’s southern headquarters at Rumangabo, six crude wooden crosses rise from a hillside.

Most of the graves belong to a gorilla family named Rugendo, whose 12 members were cut to five in July in the worst single assault recorded to date. The dead included the group’s leader, a gray-haired silverback named Senkwekwe who took charge of the family in 2001 when his own father was killed during clashes. The names are given to them by the rangers.

Mburanumwe learned of the massacre after a call on his cell phone from his father, who is still a ranger. The rangers cut down nearby trees, converted them into makeshift stretchers and carried the slain gorillas out of the park “up high, like kings,” Mburanumwe says.

Conservationists suspect the assailants were linked to the lucrative charcoal trade, dependent on trees chopped down illegally. It is conducted so openly that even trucks overloaded with hundreds of sacks move easily through army roadblocks.

Today, the rangers’ daily gorilla tracking expeditions have ground to a halt, with the front line of the war cutting straight through the Virunga reserve. But the rangers continue to blog about their lives on an Internet site hosted by WildlifeDirect, which helped draw in more than $260,000 of cash for equipment and salaries last year, according to the American charity.