A once-plentiful species of antelope could be wiped out after wholesale poaching triggered a dramatic change in mating behaviour.
Researchers from Kazakhstan, Russia and the UK are deeply concerned about the future of the saiga antelope (Saiga tatarica tatarica) after surveys from the air suggested numbers had fallen by 95% since the 1970s.
The antelope has now been rushed into the list of critically endangered species held by the World Conservation Union (IUCN).
The break-up of the Soviet Union has been blamed for the decline, as the removal of collective farming threw rural economies into chaos, forcing locals to rely on saiga meat to survive.
It also opened the border into China, where the horn of the male saiga is prized as an ingredient of Chinese medicine.
However, some of the most dramatic falls have happened in the last five years, even though less hunting of the saiga is thought to be taking place.
The researchers believe this may be because the depletion of male saiga has altered the behaviour of females.
Normally, a shortage of males is not necessarily a problem because one individual can mate with a large number of females. And saiga herds are organised in "harems" which should make this possible.
However, in this case, it appears that dominant female saiga have started jealously guarding their males, driving away younger females. With only a small number of females being mated, numbers of saiga have plummeted.
Dr EJ Milner-Gulland, from Imperial College London, told BBC News Online that tests on saiga carcasses hunted prior to the massive population drop suggested very few first-year females were being mated.
Their future is uncertain
She said: "No-one has ever seen an effect like this before in any other species.
"We knew that the change in numbers was so dramatic that it could have been due to a change in fecundity."
She said that active conservation programmes were unlikely to help the saiga. "We are just going to have to leave them alone to get on with it, and hope that numbers start to recover."
From analysis of historical data, it appears the saiga are capable of returning from the brink.
But Dr Milner-Gulland says the antelope experience should serve as a lesson for other species. "It's a warning - you can hunt them too much."
The saiga research is published in the journal Nature.