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NAIROBI, Kenya — Among the thick forests clinging to the sides of the steep volcanoes that straddle the borders between the Democratic Republic of Congo, Rwanda and Uganda live some of the world’s only wild mountain gorillas.

The gorillas are a critically endangered species surrounded by some of the earth’s most populated and dangerous countries. Yet a recently completed census shows that their numbers have risen by more than 25 percent.

Researchers carried out a census of the great apes across three adjoining national parks earlier this year. Their findings, published in December, reveal that the number of gorillas has increased to 480, up from 380 when the last count was done seven years ago.

Conservationists welcomed the dramatic increase.

“The mountain gorilla population has made an absolutely remarkable recovery,” said Allard Blom, director of the Congo Basin region at the World Wildlife Fund, one of the organizations that helped fund the research.

Despite the increase there are only 786 mountain gorillas in the world. An additional 302 gorillas are known to live in Uganda’s Bwindi National Park, according to a 2006 census there, and there are four orphaned apes living in a Congolese sanctuary.

“We cannot let down our guard on the conservation of these incredible animals,” said Eugene Rutagarama, director of the International Gorilla Conservation Program. “While mountain gorillas are physically strong, they are also incredibly vulnerable.”

Mountain gorillas were only discovered in 1902 but hunting, poaching and destruction of their habitat by humans meant that in the same century they were discovered they faced possible extinction. By the 1980s there were only 250 mountain gorillas left. Numbers have gradually increased but mountain gorillas remain a critically endangered species.

These days, the area where most of the gorillas live, known as the Virunga Massif, has become crowded with tourists. Both Rwanda and Uganda, which have been at peace for many years already, welcome tens of thousands of gorilla-seeking tourists every year. The visitors often spend hundreds of dollars for a few minutes of face time with the creatures in their natural habitat.

Across the border in the Democratic Republic of Congo, it is a different picture. Peace still eludes the east of this vast country and the continuous fighting has forced hundreds of thousands of people from their homes. The United Nations estimates there are perhaps 1.5 million displaced people in the provinces of North and South Kivu alone.

Many settle in rough camps in eastern Congo, close to the main city of Goma and also near the 3,000-square mile Virunga National Park, a World Heritage Site, where they go to hunt animals for meat and to cut down trees to make charcoal for sale — destroying the gorilla's habitat.

The forest is also home to a collection of armed rebel groups and militias who control the illegal charcoal trade — worth an estimated $30 million a year — and who clear precious forest for timber, farms and grazing land.

The battle for resources and survival in Congo often claims gorilla victims but in 2007 the world was horrified when 10 gorillas living in the forests of Virunga National Park were shot and killed, execution-style. The dead included six from a single family group. A photograph of a large male silverback, carried Christ-like on a litter shouldered by local villagers, was seen around the world.

Authorities arrested a former chief park warden, who was involved in the illegal charcoal trade, for the killings. New park management strengthened protection of the animals and paramilitary units were created to close down the charcoal barons — all good news for the gorillas.

Augustin Basabose, International Gorilla Conservation Program’s coordinator of species, said the population growth recorded since the previous census in 2003 was thanks to “the relentless collaborative efforts” of conservation groups and national park authorities in the three countries.

Six teams of 12 researchers spent two months crossing 620 miles of forested mountains and misty volcanoes in the Virunga Massif to carry out the census.

In March and April they visited Virunga National Park in Congo, Volcanoes National Park in Rwanda and Mgahinga Gorilla National Park in Uganda to observe the primates and collect and analyze stool samples in order to determine the health of the population.

The full findings of the census are to be published next year. But these initial results were a welcome piece of good news for conservationists and the long struggle to protect the gorilla.