Brown rats (Rattus norvegicus) in urban ecosystems: are the constraints related to fieldwork a limit to their study?

Abstract

Nowadays, the majority of human beings live in urban ecosystems, with this proportion expected to continue increasing in the future. With the growing importance of urban rat-associated issues (e.g. damages to urban infrastructures, costs of rat-control programs, rat-associated health risks), it is becoming indispensable to fill the identified gaps in knowledge on the urban brown rat regarding, among others, its density, home range, genetic structure, and infectious status. In this context, live-trapping is a crucial prerequisite to any scientific investigation. This paper assesses the main constraints and challenges regarding the urban field and describes the major steps to be considered when planning research on urban rats. The primary challenges are i) the characterization of the urban experimental unit; ii) the choice of a trapping design: the use of live-trapping in capture-mark-recapture design, in association with modern statistics, is highly recommended to answer ecological questions (although these methods, mostly developed in natural ecosystems, need to be implemented for the urban field); iii) the potential ethical considerations with regard to animal welfare and field-worker safety; iv) the building of mutually-beneficial collaborations with city stakeholders, pest control professionals, and citizens. Emphasis must be put on communication to the public and education of field-workers. One major need of modern urban rat research is a peer-validated field methodology allowing reproducibility, repeatability, and inference from urban field studies and enabling researchers to answer long-standing key questions about urban rat ecology.

Public Complaints Reflect Rat Relative Abundance Across Diverse Urban Neighborhoods

“…However, these methods are limited to understanding only the trappable rat population, as there may be many individuals that never enter traps. Other approaches, such as mark-recapture (Desvars-Larrive et al, 2018) or population genetics (Combs et al, 2018b) may help elucidate rat population size and genetic structure to evaluate or target rodent control. For example, a better understanding of the processes driving rat abundance across spatial scales will be useful in understanding the impacts of rodent control on the broader population (Gardner-Santana et al, 2009).…”

“…Because it is challenging and expensive to systematically survey large urban areas for signs of rats (Desvars-Larrive et al, 2018), municipal governments must often estimate rat abundance and the need for rodent control based on public rat complaints. However, this assumed relationship between complaints and rat abundance may instead reflect many other factors and may not accurately reflect rat abundance.…”

Rats About Town: A Systematic Review of Rat Movement in Urban Ecosystems

“…First, rat movement estimates have been derived using various methods which have a suite of limitations (see Box 1). These limitations highlight the challenges of studying the movements of not only rats (Parsons et al, 2017;Desvars-Larrive et al, 2018), but urban wildlife in general (LaPoint et al, 2015). Second, even among studies which employ similar techniques to measure movement (i.e., CMR), researchers have used a variety of models for calculating home range size (Low et al, 2013;Oyedele et al, 2015).…”

“…For example, the extent to which animals move within and utilize the environment dictates both the epidemiology of the pathogens they carry (Volkova et al, 2010;Guivier et al, 2011;Quixabeira-Santos et al, 2011) as well as the scale at which pest control efforts will have the greatest success (Bomford and O'Brien, 1995;Robertson and Gemmell, 2004;Adams et al, 2014). One of the most significant remaining knowledge gaps relevant to describing the spatial ecology of urban rats is information regarding the extent of their home range (Desvars-Larrive et al, 2018). The home range represents the area frequented by an individual (Davis et al, 1948) and typically encompasses areas used for food acquisition, mating, and rearing young (Burt, 1943).…”

Fox sightings in a city are related to certain land use classes and sociodemographics: results from a citizen science project

“…The red fox is a charismatic well-known species and therefore a suited study model. However, even for urban rats, a species not liked by many people, citizen science is nowadays considered as a research method [ 50 ]. Additionally, a new possibility of comparing data from different cities arises, when data on wildlife sightings is gathered through the same project design as it is currently done within the project “StadtWildTiere” in Zurich (Switzerland), Berlin (Germany) and Vienna (Austria).…”