How Scientists Are Solving the Mystery of What Killed Half the World's Saiga

120,000 saiga antelope were wiped out in just a matter of weeks. Here's how researchers are figuring out what happened.

When we hear about huge losses in an endangered species, it's usually over the course of several months or years, and it's often the fault of humans. But sometimes, nature can devastate a species in a way that baffles even the most seasoned conservationists.

The saiga is a type of antelope native to the steppes of Central Asia. They're critically endangered, and while conservation and anti-poaching efforts have managed to ease the numbers up in recent years, natural processes have just cut them drastically back down.

In May, a mysterious disease swept through multiple herds of saiga in Kazakhstan, decimating close to half of the population. In just two to three weeks, 120,000 of the animals dropped dead. What's even more amazing: this isn't the first time it's happened.

"It happened in 1984 and it happened in 2010," Joel Berger, a senior scientist at the Wildlife Conservation Society who studies saiga, told me over the phone. "I don't remember how many animals died in 84; in 2010 it was about 12,000."

This is the hardest the saiga have been hit by a single disease outbreak in recent history and conservationists are puzzled as to what exactly is going on, though there are a number of theories. Researchers have taken samples from the local environments where the saiga die-offs occurred, as well as from the animal carcasses. Berger said researchers on the ground found two kinds of bacteria in the soil of some areas, Clostridium and Pasteurella, both of which can be deadly, but usually only if the animal is already sick. It's a piece of the puzzle, but it's not the whole picture.

Part of what makes this mass die-off so strange is that three different populations living in three separate areas were all hit at the same time, Berger explained.

"That would be like having three different herds of the same species living in Ohio, upstate New York, and Washington, DC, and all of a sudden everybody's going down," he told me. "It's not just 120,000 animals all together, but widely, geographically disperse populations."

One contributing factor is the time of year: the saiga had just given birth, leaving the immune systems of the saiga mothers compromised, according to E.J. Milner-Gulland, the chairwoman of the Saiga Conservation Alliance and a professor of conservation science at Imperial College in London.

The saiga congregate in large, closely-gathered herds to give birth, too, which makes it easier for disease to spread from animal to animal, she said. The births all happen within a relatively short time span and the babies are quite large, which wipes out the mothers' energy. All of these factors leave a very vulnerable population of animals close together in one spot. But Milner-Gulland said this only explains part of what happened.

"In a sense, they're a bit of a species on the edge," Milner-Gulland told me in a phone conversation.

For now, it seems whatever hit the saiga has run its course, and no other populations appear to be affected, Milner-Gulland told me. In the aftermath, conservationists are eager to solve this mystery. They'll be taking those samples collected at the die-off sites and start analyzing for bacteria, viruses, and other pathogens—but that's only the first step, Milner-Gulland said.

"We'll do a bit of detective work, basically," she said.

Milner-Gulland told me they'll talk to local herders to see if there's been any unreported illnesses affecting sheep in the area. They'll look at the historical die-offs and compare weather conditions to see if that may have had an effect. They'll test insects and air samples for possible airborne diseases. And they'll check in on those herds of saiga that didn't get sick, to see if there's something different about them.

There's nothing that can be done to bring back the saiga that died, but conservationists hope a better understanding of the event might be able to help put preventative measures in place.

"If anything, this is a good wake-up call for realizing that a lot of different factors come together for conservation," Berger said. "The fact that there's international attention on a species that very few people knew about will hopefully inspire people to think more broadly about the amazing types of diversity we have on this planet and what we can do to conserve it."