This summer, we were horrified to learn that 60,000 endangered saiga dropped dead in Central Kazakhstan over the course of four days, with the total death toll for the month of May pegged at 120,000. But it was even worse than we realized: According to new estimates, at least 211,000 saiga, 50% of the species, died this spring.

Over at The New York Times, Carl Zimmer chronicles the ongoing effort to solve what has become one of the strangest wildlife mysteries of the year. At a meeting in Tashkent, Uzbekistan last week, Zimmer reports that wildlife veterinarians have now revised the saiga death toll up, nearly doubling the number of animals that died this spring.

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They’ve also put together a pretty good working hypothesis for the string of events that decimated this rare Central Asian antelope. Unusually stormy spring weather, perhaps exacerbated by climate change, weakened the saigas’ immune systems during a sensitive breeding period, allowing otherwise harmless gut bacteria to multiply like crazy, eating and poisoning their hosts from the inside out.

Pieces of this hypothesis were already on the table when we reported the dieoff in early September, but now, certain evidence seems to have grown irrefutable. Per Zimmer:

Once individual saigas became ill, they typically died within hours. Entire herds were quickly wiped out. “This is really not biologically normal,” Dr. Kock said.

Necropsies revealed internal bleeding, and blood testing showed that the saigas suffered massive infections of bacteria called Pasteurella multocida and Clostridium perfringens.

These species are normally harmless constituents of the microbiomes of many animals. From time to time, however, they can explode into deadly infections.

Combine renegade bacteria with the rough weather in May—a sudden drop in temperatures along with bitter wind chills—and many researchers think you’ve got the perfect storm of conditions (sorry, bad joke) to precipitate a mass dying.

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It wouldn’t be the first time wildlife biologists have drawn links between sudden climate change, weakened host immune systems, and opportunistic pathogens. Indeed, the saiga themselves have gone through population busts in the past, most notably a 1988 event that killed 73 percent of the Central Kazakstan herd. At the time, the leading cause of death was determined to be Pasteurella, one of the same gut bacteria caught red-handed this summer.

But if dieoffs are becoming more intense due to less predictable weather, the saiga, along with other small populations of grazing animals, could be in real trouble. After all, a species can only endure so many wipeouts before its capacity to rebound is suppressed forever.

[Read the full report over at the New York Times.]


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