If your city is getting rattier, climate change may be partially to blame.
In an analysis of 16 cities around the world, those that saw the biggest temperature rises over the years also had more rat complaints over time, researchers report January 31 in Science Advances. Increased urbanization was also connected with more rat reports. The results suggest that higher temperatures may make rats — and the diseases they can spread — even harder to keep at bay.
Rats don’t only make people jump and scream: They also chew up car wiring and eat crops and gardens. Their poop and pee contaminate food that they get into, and they can spread diseases such as leptospirosis and murine typhus. Their exploits cause around $27 billion in damage each year in the United States, and the world spends $500 million per year fighting a losing battle against the furry hordes.
Jonathan Richardson, an urban ecologist at the University of Richmond in Virginia, says that many of his colleagues had predicted that rat populations would increase with climate change. But no one had data to back up the prognosis.
Previous research has shown that when rat complaints go up, professionals trap more rats — indicating an increase in population. So, Richardson and his colleagues gathered records of complaints made about rats and pest inspection reports from 13 U.S. cities, as well as Toronto, Tokyo and Amsterdam. Then, they looked at the rates of rat complaints over an average of 12 years in each city and compared them to levels of urbanization (how little green space was present), socioeconomic status, human population density and average temperatures over time.
Within the time frames the team studied, around 70 percent of the cities got rattier, with San Francisco, Toronto, New York City, Amsterdam and Washington, D.C., showing the biggest rodent rises. The strongest factor associated with a faster rat race was the amount a city’s temperature had increased over time. The second predictor of more rat woes was increased urbanization; cities with diminishing green space saw rat complaints increase at higher rates.
The unseasonably warm winters of climate change, Richardson says, probably buy rats extra time outdoors. “An extra week or two foraging … that’s, in some cases, all a rat needs to breed one more time.” And while rats do need some natural habitat, a pocket park or tree box on the sidewalk will do the trick.
When humans and rats share space, there’s a real risk of disease, says Niamh Quinn, a human-wildlife interactions advisor at the University of California Division of Agriculture and Natural Resources in Irvine who was not affiliated with the study. “At some point there’s going to be — hopefully not, but potentially — the perfect storm, where we have all these people, all these rodents [and] not enough tools in our toolbox to manage them.” Leptospirosis, for example, can be deadly to humans and unvaccinated pets.
Warming weather also means fewer opportunities to control population numbers, says Bobby Corrigan, a rodentologist and rat consultant on the new study. There used to be a rodent season, he says. Pest managers knew to prepare for rats moving indoors in the winter and to take advantage of the season’s lower birth rates. “Now it’s all year round.”
source
