Half the World's Rare Antelope Population Died Within Weeks and No One Knows Why

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03 November 2015

More than half of the world’s population of an endangered antelope died within two weeks earlier this year, in a phenomenon that scientists are unable to explain.

At least 150,000 adult saiga antelopes were buried during a fortnight in May, but scientists say the actual figure will be significantly higher as many more carcasses were found but not counted as part of the burials. Calves were not counted, but it is thought that hundreds of thousands died too.

Known for their distinctive cylindrical snout, bulging eyes and curled horns as well as their ability to survive dramatic changes in temperature, the animals are one of the most endangered species on the planet with an estimated population of 300,000 before the die-off, which has only occurred in the plains of Kazakhstan, where 90 percent of the global population resides.

The mass mortality def ies understanding of how biological systems normally behave, scientists have said. They believe the deaths occurred too quickly to be attributed to a transmissible disease.

There are no wounds or evident trauma that would point to poaching and no obvious signs of malnutrition. Soil and water samples have not revealed any significant presence of toxins or poisoning by radiation, despite claims by Kazakhstan activists that fuel from Russian rockets could be to blame.

The most likely culprit is a bacteria called pasteurella already living in the throat of the animals, Prof. Richard Kock from the Royal Veterinary College at the University of London told the Guardian.

Although normally dormant, it is likely that an unidentified trigger caused it to change its character and “become nasty”, he said, producing toxins that could attack the antelope’s organ systems and cause death within hours.

But something must have triggered this change across the entire population; most likely a environmental factor, said Kock.

A temperature drop from 30C to -5C within 24 hours occurred in the days before the die-off, during the calving period after the animals have shedded their protective winter coats. However, similar temperature changes have occurred in previous years.

Ongoing climate change could also have had an impact, with significant temperature rises in the region in recent years, he added. Changes to vegetation and soil and the presence of toxins are being further investigated.

“It could all be down to timing. If you get your ducks all lined up in a row, something happens. Whatever it is, it has to be something that would affect all of them.”

The phenomenon is all the more notable for the 100% mortality rate recorded among some populations, an “extremely rare” event, said Kock.

“This is not really normal for a biological system. It’s bizarre, extremely rare and doesn’t make a lot of sense. Usually in a system, a proportion die and get sick,” he said.

Scientists are also investigating the potential role of a virus, but no evidence has yet emerged.

The species’ extinction could now be inevitable, warned Kock.

“It’s a question of luck at this stage. If you can lose 100 percent of a population, you’re left with a few populations and they are all affected at the same time, that’s it … If climate change is involved, the frequency [of deaths] will increase and if that’s the case then extinction could be inevitable,” he said.

Saiga antelopes are vulnerable to dramatic population loss. Just 15 years ago, the global population stood at more than 1 million, but the species has since experienced a decline of 95 percent, according to the Saiga Conservation Alliance. Previous population crashes were attributed to poaching.

Scientists, wildlife specialists, police and campaigners are now engaged in a race against time to save the species, with key figures from the different affected countries coming together with support from the UN last week to explore future measures to support the species.

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