A mysterious die-off of endangered antelopes last spring in Central Asia was even more extensive than originally thought, killing more than half of the entire species in less than a month, scientists have found.

“I’ve worked in wildlife disease all my life, and I thought I’d seen some pretty grim things,” Richard A. Kock, of the Royal Veterinary College in London, said in a telephone interview. “But this takes the biscuit.”

At a scientific meeting last week in Tashkent, Uzbekistan, Dr. Kock and his colleagues reported that they had narrowed down the possible culprits. Climate change and stormy spring weather, they said, may have transformed harmless bacteria carried by the antelopes, called saigas, into lethal pathogens.

It is a scenario that deeply worries scientists. “It’s not going to be something the species can survive,” Dr. Kock said. “If there are weather triggers that are broad enough, you could actually have extinction in one year.”