Rats increasing in number as city temperatures rise
A study published in the journal Science Advances, has found that rats are adapting well to a rise in temperatures. While many are suffering during the soaring temperatures, the little rodents are adapting well.
“In cities that have experienced the fastest warming temperatures, they tended to have faster increases in their rat numbers as well,” said Jonathan Richardson, an urban ecologist at the University of Richmond and lead author of the paper. “Females will reach sexual maturity faster. They’re able to breed more, and typically their litters are larger at warmer temperatures in the lab.”
The analysis relied on public complaints about rats as well as inspection records from 16 cities between 2007 and 2024, serving as a proxy for their population numbers. In 11 of the cities, rats surged in numbers during that period. Washington DC saw a 390% increase according to its last decade of data, followed by San Franscisco with 300%, Toronto with 186%, and New York City with 162%. A few cities did in fact see numbers falling including New Orleans, Tokyo, and Louisville in Kentucky, largely thanks to more diligent pest control.
“It’s a first step at answering this question, that if you get a bunch of rat scientists into a room we’re bound to ask each other: How might climate change play into rat populations?” said Kaylee Byers, a health researcher at Simon Fraser University in Canada, who was not part of the team that conducted the study.
Aside from physiological factors that influence breeding, the animals’ behaviour is affected by temperature. If it’s too cold, rats tend to huddle underground, especially in basements and sewers, or any subterranean built environment. When it is warmer, they emerge out, bringing food back to their nests.
Climate change is also affecting the timing of seasons. If the weather is warmer for a week or two longer into the winter, or if spring begins sooner, that gives them more time to forage. “Rats are really well-adapted to take advantage of a food resource and convert that to new baby rats that you’ll see in your neighborhood,” Richardson said.
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