Parsons, the Fordham University researcher, says that for these reasons, city rats need to be better understood. But trying to catch, tag and track them is difficult. The most commonly cited data when talking about changes in rat populations are calls to 311, New York City’s government-services and complaint line. News articles on the subject cite an increase in 311 calls about rats in the last few years. In New York City, rat-related calls increased by 10 percent last year compared to 2016. Washington D.C., Chicago and Boston have also seen increases in rat complaints in the last few years. But these calls aren’t a direct measure of the number of rats in a city. Rather, they measure the number of people who spotted a rat — then decided to make a call about it.
Article source: https://www.huffpost.com/entry/climate-change-rats-health-research_n_5cf8196be4b0e63eda94be0f