Increasing rat numbers in cities are linked to climate warming, urbanization, and human population
Jonathan L. Richardson
https://orcid.org/0000-0002-3701-2115 , Elizabeth P. McCoy
https://orcid.org/0009-0009-3897-6336, Nicholas Parlavecchio
https://orcid.org/0009-0003-4887-8074, Ryan Szykowny
https://orcid.org/0009-0002-8561-5815, [...], and Yasushi Kiyokawa
https://orcid.org/0000-0002-4335-1404+14 authorsAuthors Info & Affiliations
Science Advances
31 Jan 2025
Abstract
Urban rats are commensal pests that thrive in cities by exploiting the resources accompanying large human populations. Identifying long-term trends in rat numbers and how they are shaped by environmental changes is critical for understanding their ecology, and projecting future vulnerabilities and mitigation needs. Here, we use public complaint and inspection data from 16 cities around the world to estimate trends in rat populations. Eleven of 16 cities (69%) had significant increasing trends in rat numbers, including Washington D.C., New York, and Amsterdam. Just three cities experienced declines. Cities experiencing greater temperature increases over time saw larger increases in rats. Cities with more dense human populations and more urbanization also saw larger increases in rats. Warming temperatures and more people living in cities may be expanding the seasonal activity periods and food availability for urban rats. Cities will have to integrate the biological impacts of these variables into future management strategies.
INTRODUCTION
Commensal rats in the genus Rattus are among the most ubiquitous and important pest species. Two species (Rattus norvegicus and Rattus rattus) have near-global distributions, now occurring in every continent except Antarctica. Rats damage infrastructure, consume agricultural yields, and contaminate food supplies, causing an estimated US$27 billion in damage each year in the United States alone (1). Rats also harbor and transmit more than 50 zoonotic pathogens and parasites to people, affecting public health around the world (2, 3). Associated diseases include leptospirosis, hantavirus pulmonary syndrome, murine typhus, and bubonic plague. Rats thrive in human-dominated landscapes by exploiting resources concentrated where human population density is high (4) and are often classified as urban exploiting species. As a result, rat population densities are expected to be higher in cities than in rural areas, with the potential to negatively affect more people (5). The very presence of rats also takes a measurable toll on the mental health of people living in contact with them (6).
Municipalities and property owners have been trying to reduce rat numbers for centuries. In recent decades, efforts at suppressing or eradicating rats have primarily been through the use of lethal rodenticide chemicals or traps rather than nonlethal options that would make the environment less suitable (e.g., securing food waste and removing harborage) (7). Globally, the control efforts associated with this “war on rats” cost an estimated US$500 million every year (8). At the municipal level, the strategies and intensity of these control efforts vary widely among cities. Rodent control is also inconsistent within cities over time, as priorities shift, budgets and staff fluctuate, and new control products or approaches are introduced.
https://www.science.org/doi/10.1126/sciadv.ads6782
