At least eight rare mountain gorillas have been shot dead, striking a blow to conservation efforts.

The animals were part of a 12-member troop known to researchers as the Rugendo family and lived in a mountainous area straddling the borders of Rwanda and the Democratic Republic of Congo often visited by tourists.

The killings, in the Virunga National Park in eastern Congo, may have been intended as a warning to local conservationists who seek to prevent the commercial destruction of the region’s rainforests, the natural habitat of gorillas. The Virunga mountains are closely associated with Dian Fossey, the American zoologist, whose book, Gorillas in the Mist, became an acclaimed Hollywood film with Sigourney Weaver as Fossey.

Richard Leakey, the conservationist leading efforts to protect the mountain gorilla, said: “We believe at least eight or nine were killed. It is a very worrying development.” He said that such a toll represented, in conservation terms, “a huge percentage of the remaining population”.

After years of civil war the eastern region of the Congo is the domain of former rebel leaders, corrupt local officials and militia groups. The Congolese Government has taken few measures to curb poachers and protect its rare wildlife, particularly the great apes.

Conservation experts said that the slaughter was not the work of poachers because they would have taken the bodies and sold them as food or trophies. “Whatever the motive underlying this tragedy, the gorillas are helpless pawns in a feud between individuals,” Mark Rose, chief executive of Fauna & Flora International, said.

Instead, it is believed that the gorillas were killed to warn off environmentalists protesting over the chopping down of trees to make charcoal for heating and cooking. There has been a surge in demand for charcoal from Congo since Rwanda declared the activity illegal.

Mr Leakey, whose latest conservation organisation, WildlifeDirect, is trying to save the remaining gorilla population of eastern Congo, said he feared that corrupt local officials who should be protecting the park were involved in the charcoal business.

A 2004 census estimated that 380 gorillas, more than half of the world’s population, lived in the national park and surrounding Virunga volcanoes region. There is none alive in captivity.

This year two silverback male gorillas were shot dead in the same area, and a female was killed in May. The silverback was an alpha male. Alpha males are leaders within a group, in charge of leading the others to food and protecting them from danger. In his absence the group is often at risk.

“For such a small population the unnecessary and indiscriminate killing of four mountain gorillas is a huge loss,” the International Gorilla Conservation Programme, a partnership of conservation groups that includes the World Wide Fund for Nature, said in a statement.

History of Virunga

1925 Albert National Park (a precursor of Virunga National Park) is created by royal decree of King Alfred of Belgium. It is Africa’s first national park

1967 Dian Fossey, a zoologist, begins an 18-year study of Virunga’s gorillas

1979 Inscribed in the Unesco World Heritage List

1994 During the Rwandan genocide hundreds of armed Hutu militiamen flee across the border and set up camp in the park. The park is placed on Unesco’s World Heritage in Danger list

2006 More than 400 hippopotamuses are killed over one fortnight by the Congolese militia group Mai Mai in the park

2007 WildlifeDirect and the Frankfurt Zoological Society are the first conservation groups to enter the park since 1994

Sources: International Gorilla Conservation Programme; WildlifeDirect; United Nations Environment Programme; Times archives

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