In the past decade, urban rat populations have dramatically expanded, becoming an increasingly prevalent issue in major cities. According to a recent study led by Dr. Jonathan Richardson, a professor at the University of Richmond, the cities of Washington, San Francisco, Toronto, and New York City have experienced the highest rat population growth in the United States. This recent explosion in rat population size is often associated with poor food waste management and increased urbanization, but Richardson’s research illuminated new key factors in rat population expansion.
Kathleen Corradi is the NYC director of rodent mitigation and has been dubbed the “Rat Czar.” She explains that a rat is “the perfect urban exploiter,” meaning that “rat behavior is almost entirely fueled by human behavior”. Commensal rats (rats that live alongside humans and depend on them for shelter, food, and water) in the genus Rattus have been described as one of the most ubiquitous and creative pest species. By feeding on restaurant food waste and causing destruction to large urban infrastructures, rats contribute to structural and food-related damage, costing an estimate of $27 billion in the United States alone. The increasing difficulty of mitigating rat population growth has led the New York City Council to pass the Rat Action plan, a package of four bills that introduces new pest management standards for city residents and construction sites. The plan extends regulations from demolition sites to construction projects, which now must involve the purchase of a licensed exterminator to thoroughly treat the site. This includes trapping mice as they escape demolished buildings, as well as the inspection of new buildings to ensure they are not easily accessible to rats. While such legislation helps to mitigate the growing rat issue, the study conducted by Richardson has led experts, including the “Rat Czar”, to acknowledge that major factors influencing the expanding rat populations are outside of the control of an “immediate governance”.
New York City exemplifies Richardson’s newfound, holistic assessment of expanding rat populations. In New York City, temperatures have increased roughly 0.3 degrees Fahrenheit each decade since the 1950s and are projected to rise between 2 and 5 degrees on average by the next decade, according to the NYC Panel on Climate Change. Cities often magnify the results of global warming as heat is radiated from tall buildings that simultaneously limit air circulation. This, especially in combination with motor vehicles and running air conditioners, causes release of additional heat. As small mammals, rats must prioritize maintaining homeostasis and are therefore limited by cold temperatures during the winter. The magnified effects of global warming in cities “may extend the seasonal window for above ground foraging and active breeding periods for rats, supporting population growth”. This, in combination with other factors, such as increased urbanization, leading to more food waste and structural habitats, is believed to have caused massive spikes in rat population in major cities across the United States.
According to Richardson, “the most concerning of these connections we found is the link between climate warming and global trends, as global temperatures are beyond the control of individual cities”. Thus, while cities attempt to combat rat populations with new policies such as New York City’s Rat Action Plan, it appears that rat populations are benefiting from human impacts on the much larger scale of climate change. As urbanization increases, cities have expedited the warming of the planet through large reflective buildings and carbon dioxide emissions. Projections of continued warming in the near future causes Richardson and his colleagues to foresee that large cities will need to be prepared with more financial and resources for city dwellers as his team expects continued major increases in rat populations and activity.