Senseless - four mountain gorillas shot dead in a nature reserve

He is one of four discovered cold and blood-stained after being shot dead at point blank range, deep in the Democratic Republic of Congo. One had been set alight and was badly singed.

The biggest was this silverback adult male and group leader - nearly 6ft long, half a tonne in weight and huge arms outstretched. The others are adult females, two have young babies and the third is thought to be pregnant.

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The majestic creatures are the latest victims of seven brutal and senseless killings over the past two months in the Virunga National Park - home to an estimated 60 per cent of the 700-strong worldwide mountain gorilla population.

The reason for the killings is unclear. Poaching has been ruled out.

Traditionally, gorillas have been poached for their hands, feet, skulls - sold as grotesque ashtrays and ornaments - pelts, internal organs and babies, which can fetch thousands of pounds on the black market from private collectors.

But these four were left intact. And weeks earlier, at a similar grizzly scene, a baby gorilla was left clinging terrified to its dead mother.

As Rosalind Aveling, director of conservation for Fauna And Flora International, who has spent several years in the park, says: "This looks worryingly like an execution. But we can only speculate as to why."

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Conservationists think the apes were helpless pawns in an increasingly violent human feud, and killed by people trying to scare the dedicated wardens away from the sanctuary of the park.

They claim the protected area has been coming under increasing pressure from outside exploitation, especially from the powerful charcoal trade which wants the park's wood.

Gorillas - classed as critically endangered on the 2006 IUCN (International Union for Conservation of Nature and Natural Resources) Red List of Endangered Species - live in groups of between five and 30, usually consisting of one or two silverbacks, a couple of black backs, who act as guarding sentries, three to four sexually mature females who are bonded to the dominant silverback for life and a clutch of juveniles and infants.

The latest killing has robbed this group of its last silverback male.

"They've been reduced from a family of 12 to just a handful, with no dominant male," says Aveling. "The only option is for a young male to take over, but it's possible the whole group will dissipate.

"They're now at risk and their future is very fragile.

"But it's also a tragedy for the people of the three countries - Rwanda, Uganda and the Democratic Republic of Congo that share the range where the mountain gorillas exist - who rely on the income from the tourism they generate.

"The loss of any gorilla will have a huge impact."

Meanwhile, days after its mother was hauled off for a post-mortem at the park's laboratory, one of the babies is still missing. Its chances of survival are low.

"Gorilla babies are like humans," says Aveling. "They suckle for eight months, can't walk for six months and rely on their parents for years.

"There's a slim chance that one of the other gorillas in the group might look after it, but they'd have to find it first.

"The whole thing is particularly distressing because after more than 30 years of work in the area, conservationists had finally seen a small increase in the tiny mountain gorilla population of the Virunga National Park."

The tragedy is that their good work is now being undone at a startling rate.