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

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.

The ratting of North America: A 350-year retrospective on Rattus species compositions and competition

While the impacts of black (Rattus rattus) and brown (Rattus norvegicus) rats on human society are well documented-including the spread of disease, broad-scale environmental destruction, and billions spent annually on animal control-little is known about their ecology and behavior in urban areas due to the challenges of studying animals in city environments. We use isotopic and ZooMS analysis of archaeological (1550s-1900 CE) rat remains from eastern North America to provide a large-scale framework for species arrival, interspecific competition, and dietary ecology. Brown rats arrived earlier than expected and rapidly outcompeted black rats in coastal urban areas. This replacement happened despite evidence that the two species occupy different trophic positions. Findings include the earliest molecularly confirmed brown rat in the Americas and show a deep ecological structure to how rats exploit human-structured areas, with implications for understanding urban zoonosis, rat management, and ecosystem planning as well as broader themes of rat dispersal, phylogeny, evolutionary ecology, and climate impacts.

Understanding Community Perceptions of the St. Kitts’ “Monkey Problem” by Adapting Harm Reduction Concepts and Methods

Wicked problems in One Health are associated with dynamicity and uncertainty that require experts, authorities and community members to reach for innovative means of collective inquiry, and collaborative interventions to address the deep social issues at the root of interspecies problems. In this study we explore the value of harm reduction concepts to understand a hundreds of year old issue, the St. Kitts’ “monkey problem,” which involves the invasive African green monkey (Chlorocebus sabaeus) as the cause of deleterious effects on agriculture, but concurrent positive effects on tourism and biomedical research. The harm reduction approach, a systems and settings-based approach with decades of success in public health, can serve as a framework to produce action on persistent societal problems. Harm reduction concepts and methods and participatory epidemiology were used to uncover local perceptions about human-monkey interactions and “meet people where they are” by asking the research question: Are there commonalities in perceptions and values linked to the St. Kitts’ “monkey problem” that are shared across diverse representatives of society that can act as a common starting place to launch collaborative responses to this invasive species? Through a series of focus group activities and interviews we found that the Kittitian “monkey problem” is a contentious and dichotomous problem pervasive in most of society that has no single stakeholders nor one solution. Harm reduction helped to map the island’s human-monkey system and elucidated an entry point toward tackling this problem through the identification of shared values, and also provided a model for incremental gains that may be achieved. Likening the St. Kitts “monkey problem” to a wicked problem enabled stakeholders to seek more options to manage the problem rather than to conclusively solve it. Frequently mentioned shared values including the protection of farmer crops and backyard harvests likely represent strong entry points to this problem and a jumping-off point to begin collective action toward future improvements.