iStockphoto
Rat populations are growing out of control in cities across the United States and the problem is only going to get worse unless something is done. Because of this, a team of urban ecologists recently undertook a study to better understand the problem.
“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,” the study’s authors wrote in their paper published in the journal Science Advances.
In their study, the researchers used public complaint and inspection data from 16 cities around the world to estimate trends in rat populations. What they learned is that in 11 of the 16 cities (69%) there were “significant increasing trends” in rat numbers. Just three cities experienced a decline in their rat population.
“Cities experiencing greater temperature increases over time saw larger increases in rats,” the study’s authors wrote. “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.”
The cities where rat numbers increased the most during the study period (an average of 12 years) were Washington, D.C., San Francisco, Toronto, New York City, and Amsterdam. Those cities were followed by Oakland, Buffalo, Chicago, Boston, Kansas City, and Cincinnati. Tokyo, Louisville, and New Orleans were the only cities in the study where the rat population decreased. Dallas and St. Louis did not show a significant change in either direction.
Cities that had a greater rise in temperature over time and cities with less vegetation experienced greater increases in rats. Human population density, mean minimum temperature, and lower gross domestic product (a proxy of socioeconomic resources available to implement rat control efforts) were also contributors to a growing rat population.
“Controlling climate change itself requires international collective regulations to limit increased warming, which is outside of the ability of individual cities. Furthermore, slowing human population growth in cities is also unlikely, given the global trends of people shifting to a more urban distribution. Therefore, the management of urban rats will need to focus on aggressive strategies that cities can implement to slow the increase of rat numbers that is likely to continue,” the study’s authors concluded.