Rat infestations are increasing all around the world, and scientists suggest that climate change may be to blame. Publishing their results in a recent Science Advances article, a team of researchers analyzed rat populations in 16 cities from around the world, including New York, Boston, and Washington, D.C.
Their analysis — one of the first to assess rat populations at such scale — revealed that the cities that saw bigger bumps in temperatures were also the cities that saw bigger bumps in rats.
“Cities experiencing greater temperature increases over time saw larger increases in rats,” the study stated. “Warming temperatures and more people living in cities may be expanding the seasonal activity periods and food availability.”
Tracking Rats
In cities around the world, rats pose a problem. Destroying infrastructure and consuming and contaminating food, these rodents are also vectors for pathogens and parasites, capable of spreading over 50 different infectious agents to humans.
Scientists suspect that the number of rats in cities is increasing. But scientific surveys into the trends in rat populations are rare. Scurrying out of sight, in tight spaces and sewers, rats are tough to spot, making it almost impossible to assess whether rat control strategies, which differ from city to city, work.
To reveal whether rat populations are actually increasing, a team of researchers turned to public complaints and inspection information — valuable proxies for the population of rodents in a particular area. Tracking these sightings across 16 cities for an average of 12.2 years, they found that 11 out of 16 cities (or 69 percent) saw increases in rats, while 3 out of 16 cities (or 19 percent) saw decreases.
Read More: Is it Time to Change Tack in the ‘War on Rats’?
Increase in Temperature, Increase in Rats
Of all 16 cities, Washington, D.C. saw the largest increases in rat sightings, which were around 3 times bigger than those in Boston and 1.5 times bigger than those in New York.
Running the numbers on the increases, the researchers found that around 40 percent of the rise in rodent sightings was tied to the increase in temperatures relative to long-term averages. In other words, around 40 percent of the rise was tied to warmer weather, which may provide rats more opportunities to forage for food and reproduce.
“Warmer temperatures, particularly during cooler seasons of the year, may release rats from physio-thermal limitations,” the study stated. “This can be due to a combination of lower winter mortality, longer periods of aboveground activity and foraging, and increased fecundity.”
Read More: How to Coexist with Coyotes in Your Neighborhood
Making Space and Food For Rats
Beyond temperatures, the researchers found that other factors were associated with rat sightings, too: While increasing urbanization was linked to approximately 34 percent of the population boom in the rodents, increasing population density was linked to approximately 19 percent.
“This may be related to both the habitat preferences of rats and food availability,” the study stated. As cities urbanize and increase in density, more buildings and underground utilities become spaces for rats, and more food becomes available for rodents to eat.
According to the researchers, warming, urbanization, and population density are all set to increase in the coming years, amplifying the need for cities to implement new strategies for rat management.
“Given the projections of continued warming for the foreseeable future, cities need to be prepared for the potential for this warming to exacerbate current rodent pest infestation levels,” the study stated.
Rather than removing the rodents that are already in cities, the strongest rat management strategies tend to make city survival more challenging, removing the trash and the clutter on which rats rely.
“The management of urban rats will need to focus on aggressive strategies that cities can implement to slow the increase of rat numbers,” the study stated. If not, well, we’ll all need to warm up to the idea of a world with more rats.
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Science Advances. Increasing Rat Numbers in Cities are Linked to Climate Warming, Urbanization, and Human Population
Infection Ecology & Epidemiology. Rat-Borne Diseases at the Horizon. A Systematic Review on Infectious Agents Carried by Rats in Europe 1995–2016
Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
