Rat infestation in many world cities appears to be soaring, especially in Washington, and a new study blames climate change, urbanization, and other human actions. A first-of-its-kind examination of trends and reasons in hard-to-count rat populations uses sighting reports in 16 cities around the world, the AP reports. In 11 of those cities, complaints about rats have increased, according to a study in Friday's journal Science Advances. Washington, DC, was by far the leader in rat increases, followed by San Francisco, Toronto, New York City, and Amsterdam.
Washington's rising rat reporting trend was three times greater than Boston's and 50% more than New York's, the study said. Only three cities saw significant decreasing trends—New Orleans, Louisville, and Tokyo—with the home of Mardi Gras showing the biggest drop in rat reporting. Experts said the Louisiana city can teach others how to combat the rat problem. Researchers did a statistical analysis of the rising rat reporting in those cities and concluded that slightly more than 40% of the trend seen is due to warming temperatures from the burning of coal, oil, and natural gas, per the AP. And that comes down to reproduction and food, said study lead author Jonathan Richardson of the University of Richmond.
The increase is showing up in cities that are warming the fastest, he said, "probably because this is a small mammal that has physiological challenges in the cold weather months." A warming climate could give rats more time to forage above ground and possibly another reproductive cycle or two. Female rats can have a litter every month, and each litter is eight to 16 baby rats. "That is a recipe for accelerated population growth," Richardson said. Researchers also saw links to the increase in urbanization and more densely populated cities. "The rat is the third most successful mammal behind humans and house mice. So it evolved and engineered to live alongside us," New York City rat czar Kathleen Corradi said. "They followed humans, Homo sapiens, across the continents and are in every single continent except Antarctica. So it's considered a wicked problem."
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