Species towards extinction
There was almost something biblical about the scene of devastation that lay before Richard Kock as he stood in the wilderness of the Kazakhstan steppe. Dotted across the grassy plain, as far as the eye could see, were the corpses of thousands upon thousands of saiga antelopes. All appeared to have fallen where they were feeding.
Some were mothers that had traveled to this remote wilderness for the annual calving season, while others were their offspring, just a few days old. Each had died in just a few hours from blood poisoning. In the 30°C heat of a May day, the air around each of the rotting hulks was thick with flies, theguardian.com reported.
The same grisly story has been replayed throughout Kazakhstan. In this springtime massacre, an estimated 200,000 critically endangered saiga — around 60 percent of the world’s population — died.
“All the carcasses in this one of many killing zones were spread evenly over 20km2,” said Kock, professor of wildlife health and emerging diseases at the Royal Veterinary College in London.
“The pattern was strange. They were either grazing normally with their newborn calves or dying where they stood, as if a switch had been turned on. I’ve never seen anything like that.”
The saiga — whose migrations form one of the great wildlife spectacles — were victims of a mass mortality event (MME), a single, catastrophic incident that wipes out vast numbers of a species in a short period of time. MMES are among the most extreme events of nature. They affect starfish, bats, coral reefs and sardines. They can push species to the brink of extinction, or throw a spanner into the complex web of life in an ecosystem. And according to some scientists, MMES are on the rise and likely to become more common because of climate change.
The MME that has pushed the saiga closer to extinction struck in 2015. Kock was part of an international team studying the animals as they gathered for the calving season. For most of the year, saiga are on the move, able to avoid predatory wolves and human poachers by sprinting at more than 40mph, making them one of the fastest ungulates, or hoofed animals. But once a year they put their migration on pause to calve in vast groups when the grass is at its lushest, before it is scorched by the Sun.
In 2015, the main gathering in the Betpakdala region of central Kazakhstan, an area roughly the size of the British Isles, numbered 250,000. Nearby, other groups were thousands strong. Saiga are remarkable animals. Their bulbous noses, which hang over their mouths, give these antelopes an almost comical appearance. The nose is flexible and can be inflated, helping them to breathe warm air in the freezing winters and filter air in the arid summers as they sprint with their heads down in a cloud of dust. The species has been hit by mass die-offs before. In 1981, around 70,000 died suddenly in a few days, while in 1988 another 200,000 died. The creatures are also victims of poachers.
“In 2014, we believed there were about 250,000 adults and they produced a good number of calves — perhaps a couple of hundred thousand. It looked a viable population and we’d expected a population of a million soon. There was even talk of them coming off the critically endangered list,” Kock said.
But as the scientists watched a year later, the mothers fell sick and began to drop dead. “It wasn’t as if the disease started at one end and spread — there was no time for transmission of the pathogen from animal to animal. It was too quick,” he said.
“Within two or three days, everything was dying. By the end of the week, every single one was dead.”
The scientists on the ground pinpointed blood poisoning as the cause, but were puzzled as to why whole herds were dying so quickly. After 32 postmortems, they concluded the culprit was the bacterium Pasteurella multocida, which they believe normally lives harmlessly in the tonsils of some, if not all, of the antelopes.
In a research paper published in January in Science Advances, Kock and colleagues contrasted the 2015 MME with the two from the 1980s. They concluded that a rise in temperature to 37°C and an increase in humidity above 80 percent in the previous few days had stimulated the bacteria to pass into the bloodstream where it caused hemorrhagic septicemia, or blood poisoning.