Over 200,000 Endangered Antelope Suddenly Die Thanks to … Weird Weather?

A change in humidity seems to have triggered bacteria that led to widespread death of the creatures

Newborn saiga calf nestling in the arms of a scientist of the joint health monitoring team. Photograph courtesy of the Joint saiga health monitoring team in Kazakhstan

Saiga are a critically endangered antelope species with endearing elongated snouts. But the population took a hard hit in 2015 when over 200,000 of the creatures in central Kazakhstan​ died in a span of just three weeks. Now, as Merrit Kennedy reports for NPR, a new study suggests a possible reason why.

Though it has long been thought that the bacteria Pasteurella multocida type B was to blame for the deaths, it usually harmlessly resides within the creatures. But a new study, published Monday in the journal Science Advancessuggests that a period unusual weather triggered its harmful effects.

"You went from one or two animals to within three or four days — thousands. And then they were all dead by the seventh day," Richard Kock​, professor at The Royal Veterinary College and author of the study, tells Kennedy. "The animals were showing normal behavior, normal signs, normal grazing and then suddenly they'd start looking a little bit unhappy and stop feeding. Within about three hours they were dead."

Only 30,000 of the critically-endangered antelopes survived the mass fatalities—primarily bachelor males who were further north in a lower humidity area, and females in small groups in remote areas.

In the days leading up to the deaths, a period of unusually hot and humid weather struck, Kennedy reports. Though the bacteria typically live in the animals' tonsils, this weather seemed to have somehow triggered their sudden migration to the creatures' guts, Steph Yin reports for the New York TimesSubsequent blood poisoning killed the antelopes within a few hours after they showed their first symptoms.

To identify this apparent link to weather, Kock and his team carefully ruled out many possible pathogens and toxins. The animals were not exposed to anything unusual in soil or vegetation, and were otherwise healthy until the outbreak. The only unusual factor was a ten-day period of unusually warm and humid weather directly before the deaths. These environmental conditions were also present during similar mass fatality events  in 1981 and 1988, Yin writes. But how weather triggered such events remains unclear.

The 100 percent fatality rate for creatures was unprecedented. “I’ve worked with many nasty things,” Kock tells Yin. “You always get survivors.” The unusual weather hit during the antelopes’ calving period, which may have enhanced the mortality rate as females are particularly vulnerable after giving birth.

Saigas’ elongated snouts may have also played a role in why so many animals died. Their curved snouts facilitate heat exchange and keep out dust common on Eurasian steppe, Yin writes—a specialized adaptation that may make saigas more vulnerable to changing climate and environmental conditions.

While saiga herds originally roamed the Eurasian steppes in the era of mammoths, they’ve subsequently gone extinct in China and southwestern Mongolia, with the largest surviving populations living in Russia and Kazakhstan. The animals are historically robust, surviving and adapting. But although they breed rapidly, Kock fears they’re now on the verge of extinction.

"If we get a similar event, and all the animals are within a sort of weather envelope, it could be total extinction." Kock tells Kennedy. “It could happen in a week.”

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