Since the end of May, the rare saiga antelope has been dying in great numbers throughout central Kazakhstan, and scientists are just beginning to piece together the cause. According to a report from CS Monitor, a recent four day period left over 60,000 antelopes dead.

Veterinarians and conservationists rushed to ease the rate of the die-offs but got word that similar events were ongoing in other herds across the country. By the beginning of June, however, most of the deaths had ended.

The mass death of thousands of antelopes baffled scientists for quite some time, but they are getting closer to cracking the case. Bacteria are presently the key suspects, but it’s unclear as to how they were able to kill so many animals all at once.

Researchers believe that a pathogen spread throughout the entire calving herd, killing the youngest generation of animals and crashing the population. Saigas are a key component of the dry, grassy ecosystem in central Kazakhstan, decomposing a large amount of plant matter and returning nutrients back to the soil. In addition to helping prevent bushfires with their voracious appetite, they also provide a source of protein for larger predatory species.

Die-offs are becoming a common occurrence in Kazakhstan, and due to the scope and extent of the kills, veterinarians are having a hard time combing through all of the evidence. They believe that whatever pathogen was responsible was likely passed on to younger generations in the mothers’ milk.

Most of the saigas suffered from internal bleeding that could have been caused by Clostridia bacteria. The scientists explored the possibility that a genetic mutation could have made the saigas susceptible to an otherwise harmless microbe, but they have considered environmental factors as well.

The mass die-offs remain a mystery, but hopefully researchers will be able to pinpoint a cause and act to prevent future similar events.