> Prof Stenseth and his colleagues do not think a rat reservoir was to blame. They compared tree-ring records from Europe with 7,711 historical plague outbreaks to see if the weather conditions would have been optimum for a rat-driven outbreak. He said: “For this, you would need warm summers, with not too much precipitation. Dry but not too dry. And we have looked at the broad spectrum of climatic indices, and there is no relationship between the appearance of plague and the weather.” Instead, the team believes that specific weather conditions in Asia may have caused another plague-carrying rodent - the giant gerbil - to thrive.
http://www.bbc.com/news/science-environment-31588671