In May 2015, more than 200,000 saiga antelopes mysteriously dropped dead across a field nearly the same size as Britain over a period of just three weeks.
Even experienced scientists were stumped at this massive die-off that killed half of the entire species in Kazakhstan.
Although they were unable to provide an exact cause behind the phenomena, they already had their suspicions pinned on a lethal pathogen.
Now, three years after, a study confirms the previous theory to be correct. Multiple strands of evidence show that a bacteria called Pasteurella multocida attacked the saigas from the inside, causing death in a matter of a few hours.
This pathogen naturally exists inside the animal's tonsils and, in this case, somehow began to invade their guts, causing blood poisoning and organ failure.
How the harmless bacteria turned deadly remains unclear to scientists, but they believe that it was triggered by increased humidity and temperature levels brought on by climate change.
One proof is that these massive die-offs have only started occurring in the 1990s, right when environmental conditions also began deteriorating.
With only 50,000 saigas left, there is an immediate need for scientists to determine how the warming world will affect these critically endangered animals.
Environmental Change Could Result In Mass Mortality
In the study, scientists identified P. multocida to be the immediate cause of death, as no other significant pathogens were found in the soil or plants that the saigas were exposed to.
They then compared the die-off with two other similar events in 1981 and 1988, when relative humidity 10 days before the event were greater than 80 percent.
This correlation proves that the environmental change indeed triggered the bacteria to become harmful, but scientists were unable to discover how.
Biological Factors May Have Contributed To Outbreak
The animal's unique life history could also be another contributing factor. Most of the saigas that died in 2015 were newborns and mothers, as it was calving season.
Apparently, the species has unusually large calves, making the birthing process stressful for females. It also makes them more prone to contracting diseases.
Moreover, this breed of antelopes has developed certain mechanisms to adapt to the Eurasian steppe's volatile weather conditions.
For instance, their Seussian trunks facilitate the exchange of heat while protecting them from dust. This ability, however, makes the animal more sensitive to environmental changes.
Normally, the antelopes form herds comprised of 30 to 40 animals, but during migration season, they travel in tens of thousands, forming one of the most majestic migrations in the animal world. While this sight may seem a rarity nowadays, in the early 1990s, it was entirely possible, as millions of saigas were still in existence.