More rodents are infesting cities as scientists say warmer temperatures mean more rat babies

WASHINGTON (AP) — Rat infestation in many world cities appears to be soaring, especially in Washington, and a new study blames warming temperatures, urbanization and other human actions.A first-of-its-kind examination of trends and reasons in hard-to-count rat populations uses rat sighting reports in 16 cities around the world.In 11 of those cities, rat complaints have increased, according to a study in Friday’s journal Science Advances.Based on individual trends within cities, Washington 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.Washington city officials did not respond to requests for comment.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.And that comes down to sex and food, said study lead author Jonathan Richardson, a biologist at the University of Richmond.“We’re seeing these increasing trends in rats in cities that are warming the fastest, probably because this is a small mammal that has physiological challenges in the cold weather months,” Richardson said.

“If we’re warming the climate and winter starts a week or two later and spring arrives a week or two earlier, that’s one, two, maybe even three or four weeks across the entire year where those rats can be above ground foraging, acquiring more food and maybe squeezing out one or two more reproductive cycles.”An extra month may not sound like much, but female rats can have a litter every mo...