In May 2015, more than 200,000 seemingly healthy saiga antelopes in the central steppes of Kazakhstan suddenly dropped dead.
For the animals, and those charged with their conservation, the Mass Mortality Event was devastating. In the space of a few short weeks, something wiped out more than 60 per cent of the species’ global population, and more than 80 per cent of the saiga in the Betpak-Dala region. The scale of the disaster was clear. Its cause was anything but.
Saiga are exquisitely adapted to life on the Central Asian steppe, where temperatures can swing dramatically. Its most striking adaptation is its big, bulbous nose. Its convoluted nasal passages help filter out dust and cool the blood in summer, while warming freezing air before it reaches the lungs in winter.
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In the mid-20th century, mind-bogglingly huge herds of saiga roamed the region. But then decades of hunting, habitat destruction and other pressures sent numbers plummeting. By 2003, just 21,000 remained in Kazakhstan. Conservation efforts brought them back from the brink. Then, in 2015, the deaths began.
Autopsies revealed that the animals had perished from haemorrhagic septicaemia, a severe infection caused by the bacterium Pasteurella multocida. The strange thing was that this bacterium normally lives harmlessly in the saigas’ tonsils. So, what caused a usually benign bacterium to become deadly?
The answer was a perfect storm of weather and timing. The incident struck during the saigas’ calving season, when females were pregnant or had recently given birth. Then came unusually warm and humid weather. Together, the conditions appear to have allowed the bacteria to multiply rapidly and invade the bloodstream, leading to sepsis and death. It was one of the largest mass mortality events ever recorded in a wild mammal.
Since then, their numbers have rebounded. But as the world warms, conservationists fear that the perfect storm that once killed hundreds of thousands could happen again.
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