In this task, you are given a text of many news articles seperated by special token "|||||". Your task is to summarize them.

ASTANA, Kazakhstan, Sept. 4 (UPI) -- The plains of central Kazakhstan are littered with dead antelope, 60,000 of them -- an entire herd wiped out in just four days. And no one is exactly sure how or why. 
  
 The herd's collapse was bookended by a series of less dramatic die-offs, stretching from May through June. All told, the country's population of saiga, an antelope species found in the Eurasian Steppe, was halved -- from 257,000, counted in 2014, to less than 125,000. 
  
 For months, scientists have been stumped, but new evidence suggests bacteria is to blame. Still, questions abound. 
  
 The bacteria of interest, Pasteurella and Clostridia, were found in tissue samples collected from many of the felled saiga. But the microbes are common in antelope intestines and thought to be harmless. Nonetheless, toxins produced by the normally humdrum bacteria appear to have caused internal bleeding. 
  
 What's different about these microbes? According to genetic analysis, nothing. 
  
 "There is nothing so special about it. The question is why it developed so rapidly and spread to all the animals," geoecologist Steffen Zuther, a researcher with the Altyn Dala Conservation Initiative, told Live Science. 
  
 At the moment, scientists can't explain what transformed the benign bacteria into a plague-like killer. 
  
 Previous research has shown that for some animals, wild swings in population numbers are normal -- and that species such as the Canadian snowshoe hare have evolved to withstand such dramatic fluctuations. It's possible the saiga is one of those species. 
  
 Still, conservations and ecologists are worried by the endangered antelope's decline. The species helps maintain the natural order in the grasslands of Eurasia, helping thin the grass and return the nutrients of mature plants back to soil. Cold winters slow down the natural decomposition of organic matter. 
  
 Saiga hunting is banned in Kazakhstan, but researchers say more needs to be done to protect the species. ||||| In May 2015, nearly half of all the saigas, a critically endangered antelope that roams the steppe of Kazakhstan, died off. Exactly why is still a mystery. 
  
 It started in late May. 
  
 When geoecologist Steffen Zuther and his colleagues arrived in central Kazakhstan to monitor the calving of one herd of saigas, a critically endangered, steppe-dwelling antelope, veterinarians in the area had already reported dead animals on the ground. 
  
 "But since there happened to be die-offs of limited extent during the last years, at first we were not really alarmed," Zuther, the international coordinator of the Altyn Dala Conservation Initiative, told Live Science. 
  
 But within four days, the entire herd — 60,000 saiga — had died. As veterinarians and conservationists tried to stem the die-off, they also got word of similar population crashes in other herds across Kazakhstan. By early June, the mass dying was over. [See Images of the Saiga Mass Die-Off] 
  
 Now, the researchers have found clues as to how more than half of the country's herd, counted at 257,000 as of 2014, died so rapidly. Bacteria clearly played a role in the saigas' demise. But exactly how these normally harmless microbes could take such a toll is still a mystery, Zuther said. 
  
 "The extent of this die-off, and the speed it had, by spreading throughout the whole calving herd and killing all the animals, this has not been observed for any other species," Zuther said. "It's really unheard of." 
  
 Crucial steppe players 
  
 Saigas play a critical role in the ecosystem of the arid grassland steppe, where the cold winters prevent fallen plant material from decomposing; the grazing of the dog-size, Gonzo-nosed antelopes helps to break down that organic matter, recycling nutrients in the ecosystem and preventing wildfires fueled by too much leaf litter on the ground. The animals also provide tasty meals for the predators of the steppe, Zuther said. [Images: Ancient Beasts of the Arctic] 
  
 "Where you find saiga, we recognize also that the other species are much more abundant," Zuther told Live Science. 
  
 Saigas, which are listed as critically endangered by the International Union for the Conservation of Nature, live in a few herds in Kazakhstan, one small herd in Russia and a herd in Mongolia. The herds congregate with other herds during the cold winters, as well as when they migrate to other parts of Kazakhstan, during the fall and spring. The herds split up to calve their young during the late spring and early summer. The die-off started during the calving period. 
  
 Die-offs of saigas, including one that felled 12,000 of the stately creatures last year, have occurred frequently in recent years. But the large expanse of the country affected by last year's die-off meant veterinarians couldn't get to the animals until long after their deaths. The delay hindered any determination of a cause of death, and researchers eventually speculated that an abundance of greenery caused digestion problems, which led to bacterial overgrowth in the animals' guts. 
  
 Detailed analysis 
  
 This time, field workers were already on the ground, so they were able to take detailed samples of the saigas' environment — the rocks the animals walked on and the soil they crossed — as well as the water the animals drank and the vegetation they ate in the months and weeks leading up to the die-off. The scientists also took samples of the ticks and other insects that feed on saiga, hoping to find some triggering cause. 
  
 The researchers additionally conducted high-quality necropsies of the animals, and even observed the behavior of some of the animals as they died. The females, which cluster together to calve their young, were hit the hardest. They died first, followed by their calves, which were still too young to eat any vegetation. That sequence suggested that whatever was killing off the animals was being transmitted through the mothers' milk, Zuther said. 
  
 Tissue samples revealed that toxins, produced by Pasteurella and possibly Clostridia bacteria, caused extensive bleeding in most of the animals' organs. But Pasteurella is found normally in the bodies of ruminants like the saigas, and it usually doesn't cause harm unless the animals have weakened immune systems. 
  
 Genetic analysis so far has only deepened the mystery, as the bacteria found were the garden-variety, disease-causing type. 
  
 "There is nothing so special about it. The question is why it developed so rapidly and spread to all the animals," Zuther said. 
  
 Mystery endures 
  
 A similar mass die-off of 400,000 saigas occurred in 1988, and veterinarians reported similar symptoms. But because that die-off occurred during Soviet times, researchers simply listed Pasteurellosis, the disease caused by Pasteurella, as the cause and performed no other investigation, Zuther added. 
  
 So far, the only possible environmental cause was that there was a cold, hard winter followed by a wet spring, with lots of lush vegetation and standing water on the ground that could enable bacteria to spread more easily, Zuther said. That by itself doesn't seem so unusual, though, he said. 
  
 Another possibility is that such flash crashes are inevitable responses to some natural variations in the environment, he said. Zuther said he and his colleagues plan to continue their search for a cause of the die-off. 
  
 Follow Tia Ghose on Twitterand Google+. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science. ||||| Sergei Khomenko/FAO 
  
 Nearly half of the global population of the critically endangered saiga antelope (Saiga tatarica) is feared dead in a mass die-off. Authorities in Kazakhstan, where the animals live, began to notice a spike in deaths in mid-May and losses quickly mounted to more than 120,000 in total. Nature digs into what may be killing the animals. 
  
 What is a saiga? 
  
 The saiga is a nomadic antelope that lives in large herds, sometimes comprising thousands of individuals, on the steppe grasslands and semi-arid deserts of central Asia. The fossil record reveals that their prehistoric range stretched from the United Kingdom to Alaska1. But in the past few centuries, the animals have been reduced to four discrete populations: one in Kalmykia in the southwest corner of Russia and three in Kazakhstan. There is a population in Mongolia, but these animals are considered a separate subspecies (S. tatarica mongolica). 
  
 How significant are the latest losses? 
  
 Saigas are known to be prone to massive, as yet unexplained die-offs. These usually occur when the females come together to calve in the spring. In 1984, such an event in the Ural Mountains resulted in the loss of 100,000 animals — 67% of the local population. There were several smaller scale die-offs in the 2000s. But this year’s mass-death event among animals living in the Betpak-Dala region of Kazakhstan is much more significant as entire herds are dying. 
  
 “I have worked in veterinary diseases all my career and I have never seen 100% mortality,” says Richard Kock, a wildlife veterinarian at the Royal Veterinary College in Hatfield, UK, who flew out to Kazakhstan last month to assist with efforts to make sense of the devastation. “We had a herd of 60,000 aggregated and they all died. That is extraordinary.” 
  
 Do we know the cause of these die-offs? 
  
 Nobody collected detailed data for past events, so there was no way to address this question. But since the 2010 die-off, the Kazakh authorities — assisted by the United Nations' convention on migratory species and the wider international community — have been strengthening their capacity to collect, process and analyse samples from the field. “We managed to do full necropsies on 50 saiga,” says Kock, who returned from Kazakhstan on 28 May. 
  
 The cause is unlikely to have been an infectious agent that was transmitted from one animal to the next. “Epidemiologically, you cannot get a directly transmitted disease to kill a whole population in seven days,” says Kock. “I’d say it’s a polymicrobial disease,” he says. This involves pathogens such as pasteurella and clostridia that are often present in the body but have seized an opportunity to run riot. 
  
 The pathogens may have been responsible for the deaths, but something must have caused the saigas to fall victim to them. Given that two discrete sub-populations some 300 kilometres apart suffered similarly and simultaneously, it seems likely that an environmental factor is part of the story. 
  
 Why is this work important? 
  
 With a better understanding of the constellation of factors that probably lies behind such mass mortality, it might be possible to avoid such events in the future. “This time is the first time we are going to be able to get a good diagnosis,” says E. J. Milner-Gulland, a conservation biologist at Imperial College London and chair of the Saiga Conservation Alliance. 
  
 This is important because mortality on this scale can wipe out entire herds. In some ways, it is fortunate that the Betpak-Dala population was hit this time. “It’s the largest population and can probably stand it. All the other populations are at such a low level that they could be wiped out within a week,” says Milner-Gulland. 
  
 Why is the saiga in such trouble? 
  
 Towards the end of the nineteenth century, widespread hunting brought the species close to extinction. There was some recovery in the twentieth century, but the end of the Soviet era brought about a dramatic collapse. With rural poverty, a willing market for meat and horns in China and little law enforcement or management, people killed saigas in huge numbers. “Those three things together caused a 95% decline over a ten-year-period,” says Milner-Gulland. 
  
 Owing to this precipitous decline, the saiga is listed on the International Union for Conservation of Nature's Red List of Threatened Species in one of the highest categories: critically endangered. 
  
 At the latest count, announced in April 2014, the global population stood at 262,000, up more than 200,000 from the lowest point in the early 2000s. Much of that increase was driven by growth in the population that is now being devastated. |||||
An already critically endangered species has been driven even further to the brink after an insane population decline compounded by the fact that scientists are at a loss to explain it. Initially, scientists weren’t too perturbed to hear some saigas—a type of antelope that inhabits Kazakhstan, Russia, and Mongolia—were dying off during their calving period in May; some 12,000 died of apparent digestive issues last year after scientists speculated that there was too much greenery, reports Live Science. But suddenly, at least 120,000 animals, or half of Kazakhstan’s population, were dead by June, including a herd of 60,000 saigas felled in four days. "I have worked in veterinary diseases all my career and I have never seen 100% mortality," an expert tells Nature. "That is extraordinary." Another adds the "extent" and "speed" of the die-off "has not been observed for any other species...It's really unheard of." Researchers quickly moved to identify the threat, following what little clues they had: Necropsies and observations showed mothers died first, followed by their calves. But a most mysterious find came next: Scientists found toxins from the usually-harmless Pasteurella and possibly Clostridia bacteria often found in the animals’ bodies were causing extensive bleeding in their organs, per UPI. What had changed in the bacteria to make it suddenly deadly? Apparently, nothing. "There is nothing so special about it. The question is why it developed so rapidly and spread to all the animals," a researcher says. Experts are continuing to investigate but say the die-off may be another "flash crash" like the 1988 die-off of 400,000 saigas; bacteria may have spread more easily this year via standing water after a wet spring; or the Pasteurella and Clostridia bacteria may have suddenly sprung into unexpected action. (Alaska's whales aren't faring well, either.)