Living with Rats: Could an Ecosystem Lens Provide New Insights into Urban Rat Control?

Chelsea Gardner Himsworth

THE RAT PROBLEM

Brown rats (Rattus norvegicus, henceforth referred to as rats) have coexisted alongside people for millennia. They are one of the most ubiquitous animal species on the planet. Having spread around the world in association with human transport, rats are now found throughout every continent except Antarctica (Feng and Himsworth, 2014). Rats are unique among free-ranging wildlife in that they not only tolerate human presence, they thrive on it. Indeed, rats are so well adapted to utilizing human resources that they are seldom found outside of human habitations (Feng and Himsworth, 2014). Cities, in particular, provide optimal rat habitat. High human population densities provide abundant food and harborage, sustaining large numbers of rats within small geographic areas (Davis, 1953; Feng and Himsworth, 2014). Unfortunately, rats make for unwelcome bedfellows, as they have been associated with several negative consequences for humans. Rats can damage infrastructure and contaminate and consume food stuff; they are a source of a number of infectious diseases (Wundram and Ruback, 1986; Himsworth et ah, 2013; Himsworth and Feng, 2014). Given global trends towards urbanization and densification, urban rat-related issues are more than likely to increase in the future (Parsons et ah, 2018).

When one considers the fact that human communities have been trying to rid themselves of rats since almost the dawn of civilization, it is surprizing that the

“rat problem" persists. Indeed, rats have proven themselves virtually impossible to extirpate. This may be partially due to the characteristics of the rats themselves. They are highly exploratory, opportunistic, and adaptable, which allows them to exploit a broad range of resources (Barnett, 1976; Colvin and Jackson, 1999). However, they are also neophobic and can learn from negative experiences, which decreases the efficacy of traps and poisons (Barnett, 1976; Clapperton, 2006). Finally, they reproduce at a staggering rate, therfore infestations are quick to become established and, after a control attempt, the infestation can quickly rebound to pre-control levels (Davis, 1953; Colvin and Jackson, 1999). So, is it any wonder that many cities seem to be plagued by rats? Or do the cities themselves bear some responsibility for their rat problems?

COMMON ISSUES WITH URBAN RAT CONTROL AT A MUNICIPAL LEVEL

There are three major areas in which cities tend to err in their approach to rats. The first is a lack of good governance or strategic planning (Colvin and Jackson, 1999). Rat-related issues are often addressed through a hodgepodge of unrelated policy and programming. Thus, municipal governments may respond only to infestations that occur on public properties or in scenarios requiring permitting (i.e. demolition), while local health authorities may respond only to infestations in food-producing establishments or where there is a demonstrated health risk. At best, municipal leadership is highly fragmented, at worst it is absent altogether. For most of the urban landscape, people are left to fend for themselves.

The second problem is the dearth of urban rat surveillance tools and techniques, in combination with the fact that decision-makers frequently focus on action even in the absence of knowledge. Data collection is often neglected in the design and execution of municipal rat control interventions, so much so that there is usually not enough information to answer even the most basic questions like: "How many rats are there? Where do they live? Why are they there? Is the problem getting worse?” Without this information, it is virtually impossible to efficiently allocate resources, to design informed and effective policies and programmes, or to assess the return on investments. After all, without knowing what the rat problem looked like beforehand, there is no way of knowing whether an intervention made the problem any better.

This leads to the third problem: the “ambulance approach” to rats. Without data or strategy for guidance, the most common response to rat infestations is to wait until they are causing a significant problem and then swoop in and try to trap or poison as many animals as possible. This reactionary approach is probably the least effective w'ay to deal with rats and is rarely successful at controlling or eliminating infestations in the long term (Clinton, 1969; Colvin and Jackson, 1999; Himsw'orth et al., 2013). Additionally, waiting for an infestation to reach a critical threshold before there is an intervention is neither the most efficient nor the most effective point at which to intervene, and this approach completely precludes any possibility of preventing infestations before they occur. We need only to look to preventative medicine, our current standard of health care, to see the value of the idea that "an ounce of prevention is worth a pound of cure,” and that it is never a good idea to wait until someone needs an ambulance before dealing with their health problems.

Some might argue that ecologically based rodent management (i.e. pest control techniques that incorporate an understanding of the biology and ecology of rodents and the environment in which they reside) is the panacea to the urban rat problem, and that the reason it has not been widely adopted in urban centres is a lack of political will (Singleton et ah, 1999; Colvin and Jackson. 1999). However, given that no city on any axis of space, time, or politics has yet to emerge with an efficient or effective rat management strategy, the problem may lie deeper. The problem may be fundamentally one of perspective.

 
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