Nairobi (AFP) - Warring factions in South Sudan have slaughtered, poached and eaten "alarming" numbers of endangered wildlife, devastating one of Africa's largest migrations, conservationists warned Wednesday.

Government and rebel troops, locked into a war marked by widespread atrocities in which tens of thousands of people have been killed, are pushing elephants to the brink of extinction in the young nation, said Paul Elkan from the Wildlife Conservation Society (WCS).

Elephants have been slaughtered for their tusks, while giraffe and antelope have been mowed down with machine guns for meat to feed the tens of thousands of soldiers and rebels battling each other since December.

"It is a tragedy, the conflict is having a terrible impact," Elkan told AFP from Juba, where he works with the government to set up parks and protect the wildlife.

"South Sudan's war weary elephants are now at a precipice, and the ongoing fighting threatens to push them ever closer towards national extinction."

The survival of South Sudan's wildlife was once a rare cause for hope in a land left in ruins by the decades of conflict that paved the way for its independence in 2011.

But since war broke out again in South Sudan in December last year, almost a third of elephants fitted by WCS with satellite monitoring collars are believed to have been poached.

- Wildlife in 'grave danger' -

"In less than a year we have witnessed this enormous loss," Elkan said. "This indicates that there are an alarming number of elephants being poached."

The latest war erupted when President Salva Kiir accused his sacked deputy Riek Machar of attempting a coup. Violence has escalated into an ethnic conflict involving multiple armed groups.

With gunmen shooting down aircraft -- including UN aid helicopters -- the WCS have been unable to deploy its low level flights to verify exact numbers of wildlife killed.

But Elkan, an American conservationist based in South Sudan for several years and who conducted the first aerial surveys after the end of the 1983-2005 war, said the 30 percent loss of collared elephants was "indicative" of the wider slaughter.

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"It is very clear that animal populations are getting hit very hard," Elkan said. "South Sudan's remaining elephants and other vulnerable wildlife species are in grave danger."

The government has seized 65 tusks from traffickers this year -- the deaths of at least 33 elephants -- as well as leopard skins and piles of antelope bush meat.

South Sudan had some 80,000 elephants in the 1970s, and many feared they had been wiped out almost entirely by the 1983-2005 war.

But WCS surveys found as many as 2,500 had survived against the odds, many living in the vast Sudd swamp, the largest wetland in Africa.

But the past 11 months of war has seen animals targeted on a scale not previously seen, with frontlines slicing key wildlife migration routes, compared to the last war where battles often focused around government-held garrison towns.

"The elephants found a way to survive that war, but this conflict is different," Elkan said.

Eastern Jonglei state is home to giant herds of antelope -- including tiang, white-eared kob and reedbuck -- as well as giraffe, lion, cheetah and vast bird populations.

The wilderness is the largest area of intact savannah eco-system left in east Africa, and the circular migration of animals rivals in terms of numbers that between Kenya's iconic Maasai Mara and Tanzania's Serengeti ecosystems.

But as well as shooting animals to feed troops, some commanders are selling bush meat commercially, killing thousands of the animals for profit on an industrial scale.

Wildlife was seen as a key resource for South Sudan in trying to diversify from what before the war was its almost total dependence on oil.

"The elephants and other wildlife species have huge potential to contribute to the future prosperity of South Sudan, but only if these magnificent animals survive," Elkan said.