Here’s what killed all those antelopes on the steppes. It’s warmer now.

Science News gets the answers on what suddenly killed 200,000 saiga antelopes in 2015:

“If you come at dawn and dusk, it’s magical,” says E.J. Milner-Gulland, a conservation biologist at the University of Oxford who has studied saigas for 27 years. “You hear this mewing noise, and all the babies come rushing up to the females.”

The sight that greeted Milner-Gulland’s colleagues in 2015, however, was horrific. Mothers and calves, behaving normally one day, suddenly became lethargic. Weakness, collapse and death soon followed. “It was like a switch was turned on in each animal,” says wildlife veterinarian Richard Kock of the Royal Veterinary College at the University of London. Mothers died first. Helpless calves, obviously distressed, tried to suckle from their dead mothers, but eventually succumbed hours later. In three short weeks, more than 200,000 carcasses littered the steppes.

Based on necropsy evidence and sampling for a plethora of pathogens, the team diagnosed hemorrhagic septicemia, or fatal blood poisoning, caused by Pasteurella multocida type B bacteria, the researchers report January 17 in Science Advances.

P. multocida is a normal inhabitant of the bulbous, oversized snouts of saigas. “They have it naturally in their noses, just like we all have various bacteria living harmlessly in our bodies,” Milner-Gulland says. Even newborns carry the bacteria, probably passed on from their mothers, she explains.

But higher than normal temperature and humidity, which caused the microbes to multiply, turned the bacteria deadly, according to the researchers’ statistical analysis. Milner-Gulland sees the results as a cautionary note on saigas’ future in a changing climate.

Around 107,000 saigas remain globally, Kock estimates based on a summer 2017 tally.