Rethinking urban life in the face of booming rat populations 

From deer casually crossing highways to boars rummaging through garbage in communal gardens, wildlife and humans are no longer two worlds apart. Cities now provide an almost perfect backdrop for species typically associated with lush, untouched nature. This also reminds us that – before urbanisation gradually encroached on natural landscapes – all areas existed in a wild, undisturbed state. 

When the pandemic hit and business activities shut down in 2020 wild animals were seen roaming freely in human-dominated areas, reclaiming their space and redefining the global urban landscape. Among them, rats, which have long been associated with human settlements, have quietly but steadily taken over the streets over the past centuries. 

As ecosystems become more interconnected in an ever-shrinking space, what can be done to prevent humans and wild species from colliding? 

The World Organisation for Animal Health (WOAH) recognises that human-wildlife encounters are currently on the rise, increasing the risk of disease emergence. In its 100 years of existence, the Organisation has broadened its focus to include wildlife, believing that animal health and wildlife health are integral to the planet’s life support system. 

Life in the city 

For some, it may be surprising to learn that rats are considered part of wildlife – more precisely, commensal wildlife – wild species that live close to humans. There’s still much to discover about these creatures, which are often overlooked in scientific literature.

Recently, some studies have tried to understand what it is that lures rats into the city. As urban spaces grow and resources concentrate in small spaces, rats are increasingly stepping out of their comfort zones in search of food, waste and shelter. Today, they can be found anywhere across the streetscape – from basements to construction sites and abandoned buildings – as they frantically fulfill their needs. 

But the ubiquity of this species isn’t solely due to their inquisitive nature and ability to adapt. Among the factors pushing them to human-made settings, climate change has been identified as a driving force. A new study in the journal, Science Advances explores the nexus between this extreme event and burgeoning rat populations. Big cities across Europe and the US showed the strongest positive trends, highlighting one key point: the places that saw greater increases in average temperatures are also the ones that reported larger increases in rat sightings.

A researcher at the National Institute for Public Health and the Environment (RIVM) in the Netherlands, Miriam Maas has studied rat-borne zoonoses for over 10 years. She explains that rats’ close proximity to people and their enhanced interactions pose a public health concern. Taken together, rats can carry and transmit a relatively large number of harmful pathogens. However, only a limited number of them cause significant burden in humans, which varies according to the region. This is the case for leptospirosis, which leads to the hospitalisation of 40-60 people per year in the Netherlands, while the number is much higher in subtropical regions.    

Solutions for a harmonious coexistence  

The rise of rat populations in highly urbanised settings raises critical questions about the delicate balance between ecosystems. Some cities have implemented a radical approach. In New York, for instance, a Summit was held last year for the first time, bringing together researchers from across the country and Municipal Rodent Control Experts to advance the science of urban rat management. Proposed solutions encompass education and public engagement programmes but also more drastic initiatives such as birth control and extermination.  

Taking another approach, Maas believes that changing deeply ingrained human behaviours, knowledge and perceptions is the first step towards achieving a harmonious coexistence between rats and their surrounding ecosystems. Behavioural changes including better hygiene and more informed waste management practices – from limiting their availability and providing enough waste bins – are key. This means that municipalities and the general public need to join the conversation, working together to reduce waste availability and ensure proper waste disposal. 

It also comes down to understanding shifting demographics and the role played by urbanisation, densification and climate change, among other underlying factors. “As rats cannot be eliminated from the cities, we need to establish a consensus of acceptable population sizes”, Maas continues. “For example, in parks many people are more likely to accept rats living there, whereas very near their homes, people are less likely to do so”. 

Re-imagining a shared space for everyone’s health

While wildlife presents cities with new challenges, it also offers some unique conservation opportunities. Green spaces can provide safe havens for wild animals, while wildlife-friendly facilities, such as urban gardens and restored wetlands, can help sustain local wild populations while also preserving biodiversity. 

Kaylee Byers teaches at the Faculty of Health Sciences at Simon Fraser University and leads the OH-HI (One Health, Human dimensions and Implementation) Science CoLab which explores local and global solutions that support our connected and collective health. She believes that rats do so well in our cities also because of us – the ways we have constructed our cities, the food we make available to them.   

In other words, the species evolved to thrive in the conditions provided by humans. “Fortunately, there are many steps that we can take to reduce our contact with rats,” she argues when asked about what can be done to ensure healthy interactions between wildlife and humans. This includes improving urban infrastructure and reducing access to food for them to survive.  

However, when it comes to rats, a significant stigma remains. Our fear of them is partly rooted in historical context and a general lack of understanding. It is also true that some rats are responsible for displacing and out-competing other native rodent species. For instance, the so-called “Black rat”, which is thought to have originated in India before being spread by human activities across continents, has ironically been displaced or replaced in many places by the Brown rat. The invasive nature and negative impact of some rats on native species are aspects that need be factored in.  

But as we learn more about rats – both in the wild and in the lab – we mostly see unexpected reflections of ourselves.

“Rats are social, intelligent, they can solve puzzles, act in movies and even drive tiny cars!” adds Byers. “Of course, it is important to be mindful of the health risks posed by these animals. But if we used One Health to focus more on managing the interfaces of how we interact with them this would reveal a world of possibilities that promotes the overall health and wellbeing of our urban environments”. This also includes shifting our processes from response to prevention, which can help avoid risky contact that increase chances for spillover and subsequently reduce the risk of human infection.  

Building on a similar vision, the World Organisation for Animal Health (WOAH) has recently expanded its work in wildlife health, guiding its Members in their use of One Health strategies at national level to help manage the risk of disease emergence at the human-animal-ecosystem interface and protect wild animals in these scenarios. Through the lens of the programme, WOAH works with countries to build their national capacities to monitor animal diseases and encourage One Health partnerships between different government institutions. 

As the planet continues to evolve, the story of rats booming in urban environments emphasises the interconnected nature of ecosystems, animal health and human well-being, ultimately underscoring the need for collective action. 

“The reality is that rats are here to stay,” concludes Byers. “As city populations grow, rats are likely to follow.” Their established presence opens up the urgent conversation about how to manage human-wildlife interactions in a balanced, thoughtful way. Urban rat populations teach us that the solution does not always lie in the will to “make it work”. When it comes to urban wildlife, cities must find ways to coexist with diverse species such as rats – even if that involves compromise.