A new research study led by University of Richmond biology professor Dr. Jonathan Richardson shows that the increase in rat numbers in cities worldwide is linked to a warming climate and city growth.
Trends in rat sightings across 16 cities. (GRAPHIC COURTESY OF SCIENCE ADVANCES)
Dr. Richardson and his research team analyzed public complaint and inspection data from 16 cities around the world. The team found a strong link between rising rat numbers and three key aspects of the urban environment: human population density, urbanization and warming temperatures.
Key findings in the study include:
- Eleven of 16 cities had a significant increase in rat numbers, including Washington D.C., New York City and San Francisco, Calif.
- Only three cities experienced a decline: New Orleans, La.; Louisville, Ky.; and Tokyo, Japan.
- Cities experiencing greater temperature increases over time saw larger increases in rat numbers.
- Cities with more dense human populations and more urbanization also saw larger increases in rats.
All of these factors create significant challenges for municipalities and pest management professionals working to control rat populations.
The link between warming temperatures and rat numbers. (GRAPHIC COURTESY OF SCIENCE ADVANCES)
“The most concerning of these connections we found is the link between climate warming and rat trends, as global temperatures are beyond the control of individual cities,” said Dr. Richardson.
Temperature increases may be expanding the seasonal activity periods for rats, allowing them to stay active longer into the winter and begin foraging aboveground for food resources earlier in the spring.
“Even an extra week or two of aboveground activity for wild rats can translate to one or two more reproductive bouts, accelerating population growth,” Dr. Richardson said. “Those working to manage rat populations will need to factor this climate-accelerated growth into their rat management planning.”
Identifying long-term trends in rat numbers, and how they are shaped by environmental changes, is critical for understanding their ecology and for projecting future vulnerabilities and mitigation needs.
Possible solutions for cities include:
- Invest more resources (budget and staff) to help combat the problem.
- Develop proactive rodent management plans that prioritize making the urban environment less conducive for rats.
- Start collecting systematic data on rat activity and abundance rather than relying on public complaint data.
“Only by confronting the environmental factors that allow rats to thrive, and by giving municipal rodent managers the resources and tools they need, can we hope to rein in our growing rat problem,” Dr. Richardson concluded.
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from Pest Management Professional https://www.mypmp.net/2025/02/03/study-shows-rat-populations-are-on-the-rise-thanks-to-warming-temperatures-city-growth/
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