Nautilus Members enjoy an ad-free experience. or Join now .

Dead animals were scattered across the steppe in front of us. Up to the horizon. Thousands of them. That was the moment we understood that we were observing a mass mortality of catastrophic dimensions.

We were in Kazakhstan that day in May of 2015 to study the saiga antelope, a remarkable herd animal that grazes in semideserts, steppe, and grasslands, and has evolved to run long distances at high speeds. Our team was a part of the Altyn Dala Conservation Initiative, which conducts annual observations of the endangered animal’s calving season. We had noticed a few animal carcasses, but the situation didn’t seem exceptional. The area’s saiga, after all, were known to have experienced mass die-offs in the past.

Nautilus Members enjoy an ad-free experience. Log in or Join now .

But every day, more and more animals died. And then, suddenly, in just two days, about 80 percent of the gathered herd fell dead, leaving everybody both puzzled and worried. Within another two days, the entire herd had perished.

Nautilus Members enjoy an ad-free experience. Log in or Join now .

View Video

We soon learned that other saiga herds elsewhere in the region were suffering the same fate. Some 200,000 animals would die in about one month’s time, representing about 88 percent of the Betpak-Dala saiga population in Central Kazakhstan, and more than two thirds of the global population. This was mass mortality at a scale unheard of in other ungulate species.

Fueled by posts in social media, the public quickly developed its own theories. The most popular one revolved around the space program. Rockets are regularly launched from Central Kazakhstan, and, the theory went, either crashed rockets polluted saiga habitat, or rockets dumped toxic fuel into the atmosphere during flight. Unfortunately, there really was a recent accident involving a Russian Proton rocket. But it was at high altitude, above Russian territory, and occurred a week after the saiga die-off began. No other accidents were reported around the time of the die-off, nor in the months before it. Other theories held by the public revolved around general environmental pollution, a bloom of toxic algae in lakes and rivers, and even the intentional poisoning of saiga by poachers (male saiga horns fetch high prices in East Asia).

Nautilus Members enjoy an ad-free experience. Log in or Join now .

The faster we could find out the real cause of the die-off, the more chance we had of understanding how to save the species—and of countering some of these counterproductive rumors. We put all our other work on hold. Continuing an existing collaboration among scientists from Kazakhstan, the United Kingdom, and several national and international NGOs, we focused on collecting as much evidence as possible about the incident. This included direct observations of sick and dying animals, post-mortem examinations, expeditions to calving sites and along migratory routes, laboratory tests, and data analysis.

The laboratory tests gave us an early result: The bacteria Pasteurella multocida was one agent behind the mass die-off. Surprisingly, after months of additional work, we could find no other causes. Multocida was well known, and is in fact usually present in saiga, and harmless. It had not previously been associated with such an extreme die-off. Now it was causing hemorrhagic septicaemia, killing huge numbers of animals. The question then became, what triggered it to do so in this case?

Part of the answer seems to be environmental conditions, and in particular, the weather. We noticed that both the 2015 die-off and previous die-offs were preceded by high humidity and elevated air temperatures, suggesting that these environmental factors can trigger multocida to become virulent. If that’s true, we can expect saiga to experience further distress if similar weather conditions occur again, something made potentially more likely by the warming effects of climate change.

For myself and everybody involved in the fieldwork, the 2015 saiga die-off was a horrible experience. Not only was the success of many years of conservation work washed away in just a few days, but watching such large numbers of animals dying in agony was hard to bear and burned deeply into all our memories. It is through our science, and testimonials like this essay and the video above, that we hope to keep alive the lessons of that summer and avoid similar tragedies in the future.

Nautilus Members enjoy an ad-free experience. Log in or Join now .

Steffen Zuther is a geoecologist and the international coordinator of the Altyn Dala Conservation Initiative.

close-icon Enjoy unlimited Nautilus articles, ad-free, for less than $5/month. Join now

! There is not an active subscription associated with that email address.

Join to continue reading.

You’ve read your 2 free articles this month. Access unlimited ad-free stories, including this one, by becoming a Nautilus member.

! There is not an active subscription associated with that email address.

This is your last free article.

Don’t limit your curiosity. Access unlimited ad-free stories like this one, and support independent journalism, by becoming a Nautilus member.