Story transcript

Richard Kock will never forget the time 220,000 critically endangered saiga antelope dropped dead in the fields of Kazakhstan.

The mass die-off over a three-week span in May 2015 wiped out 60 per cent of the creature's global population in one fell swoop.

"You don't forget things like that," Kock, a wildlife veterinarian and professor at the Royal Veterinary College in London, told As It Happens host Carol Off.

"One animal died, and then another one… They just continued to die like flies."

Dead saiga antelopes lie on a field in the Zholoba area of the Kostanay region of Kazakhstan on May 20, 2015. (Kazakhstan's Ministry of Agriculture via Reuters)

It was a shock for conservationists who spent years bringing the saiga back from the brink of extinction caused by poaching.

Scientists quickly identified the cause of death as blood poisoning and internal bleeding caused by a bacterial infection.

But they didn't know why it happened — until now.

Hot and humid weather is likely to blame, according to a new study authored by Kock and published in the journal Science Advances.

When good bacteria turns bad

The antelope were infected with the bacteria Pasteurella multocida, which is normally harmless, Kock said.

"These bacteria are usually good. I mean, they're very much a part of health," Kock said.

But when exposed to unusually warm and wet weather, it became deadly.

The researchers compared the May 2015 data to two separate mass die-offs of saiga in the 1980s. In each instance, the average daily temperatures were higher than normal leading up to the outbreak, and humidity was above 80 per cent.

"The bacteria like warm, wet conditions," he said.

"We think that triggered the bacteria, which were in small numbers, to proliferate in each animal across a huge landscape… These bacteria started invading into the bloodstream. Once they were there, it was blood poisoning."

Saiga graze next to carcasses of dead antelopes in May 2015. 'They just continued to die like flies,' said wildlife veterinarian Richard Kock. (Kazakhstan's Ministry of Agriculture via Reuters)

Kock said the saiga will likely recover, but they remain vulnerable.

"They're very resilient and they reproduce very rapidly," he said. "But if we have another event… if it's big enough, if the weather envelope is big enough, we could lose the entire population."

The findings, he said, could also have more widespread ramifications as the planet sees more intense shifts in climate.

"It's a warning that environmental changes can have very dramatic effects," he said. "We must take notice of it and we must be concerned about it because we're mammals as well."