They found the first carcasses in late December, on the frozen steppes of Mongolia’s western Khovd province.
By the end of January, officials in the region had recorded the deaths of 2,500 endangered saiga antelopes — about a quarter of the country’s saiga population — and scientists had identified a culprit: a virus called peste des petits ruminants, or P.P.R., also known as goat plague.
It was the first time the disease, usually seen in goats, sheep and other small livestock, had been found in free-ranging antelopes. For the saiga, an ancient animal that once roamed the grasslands of the world with the woolly mammoth and the saber-toothed tiger, the outbreak was potentially catastrophic.
The antelope’s numbers, once in the millions, have been severely depleted by illegal hunting, habitat loss and competition for food. The species is described as critically endangered on the International Union for Conservation of Nature’s Red List.