Scientists researching the population have found that in the case of the male, there are not enough antelopes to mate with the females - despite the male's polygynous practice of maintaining a harem of 12-30 females.

Data from a 10-year field study, reported in Nature, explain the drop in numbers, ranking in the World Conservation Union's category of most endangered species, as due to selective hunting for its horns, used in traditional Chinese medicine. Now females outnumber males by a ratio of 100:1.

Dr Eleanor Milner-Gulland, lead author, based in the department of environmental science and technology, explained: "Until now, in polygynous systems, it has been assumed that even when males are in short supply their ability to inseminate many females secures the viability of the population.

"However, we found dominant females were aggressively excluding the younger females from the males and preventing them from getting pregnant. Our observations indicate that if the percentage of males in the population falls below one per cent, reproductive collapse will result.

"At present, the saiga population is halving each year and the species could soon be lost. Action must be taken now to provide a sustainable future for the antelope."

Once found roaming the grasslands of Central Asia in vast herds, the global population of saiga antelope has crashed to 50,000 during the last 10 years, to five per cent of its previous size.

Researchers from the UK, Russia and Kazakhstan collected data on saiga population dynamics in Kalmykia, Russia between 1992-2002. They found that changes in population density or climatic variation did not account for the drop in the number of offspring.

The researchers concluded that the heavily skewed sex ratio must be the driving force behind the antelopes decline.

However, all may not be lost. Historical data suggests a similar population crash occurred at the beginning of the 20th century, also as a result of over hunting.

The rise of the Soviet regime closed the country's borders and a strict ban was imposed on hunting, which allowed the population to recover.

"This indicates the species is very resilient. If the population has rebounded before we hope it can do it again," concluded Dr Milner-Gulland.

"There is only one viable herd in captivity and the species is difficult to breed because of their nomadic existence and diet in the wild.

"Efforts must be focused on involving rural people in conservation and providing resources to train and equip local law enforcement agents."