Increasing rat numbers in cities are linked to climate warming, urbanization and human population

Urban rats are notorious invasive pests that thrive in cities by
exploiting the resources accompanying high human population density.
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 trend
analyses of public complaint and inspection data in 16 cities around the
world to estimate trends in commensal 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 rat numbers. 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 resource availability for urban rats.
Cities will have to integrate the biological impacts of these variables
into any future management strategies.