Rats in Sewers
Characteristics of the urban sewer system and rat presence in Seattle.
Guo X, Lee, MJ, Byers KA, Helms L, Weinberger L, Himsworth CG. 2022. Urban Ecosystems DOI: 10.1007/s11252-022-01255-2
Rats are abundant and ubiquitous in urban environments. There has been increasing attention to the need for evidence-based, integrated rat management and surveillance approaches because rats can compromise public health and impose economic costs. Yet there are few studies that characterize rat distributions in sewers and there are no studies that incorporate the complexity of sewer networks that encompass multiple sewer lines, all comprised of their own unique characteristics. To address this knowledge gap, this study identifies sewer characteristics that are associated with rat presence in the city of Seattle’s urban sewer system. We obtained sewer baiting data from 1752 geotagged manholes to monitor rat presence and constructed generalized additive models to account for spatial autocorrelation. Sewer rats were unevenly distributed across sampled manholes with clusters of higher rat presence at upper elevations, within sanitary pipes, narrower pipes, pipes at a shallower depth, and older pipes. These findings are important because identifying features of urban sewers that promote rat presence may allow municipalities to target areas for rat control activities and sewer maintenance. These findings suggest the need to evaluate additional characteristics of the surface environment and identify the factors driving rat movement within sewers, across the surface, and between the surface and the sewers.
Guo X, Himsworth CG, Lee MJ, Byers K. 2022. Urban Ecosystems 26(3): 1-10.
Rats are abundant in the urban ecosystem, posing concerns for public health, infrastructural damage, and negative impacts for other urban wildlife. Sewers are considered to be one of the main reservoirs for urban rat populations, and rats may migrate between sewers and other surface areas in search of food and harbouring sites. Yet the ecology of rats in sewers has received little attention. To address this knowledge gap, this review identifies a number of sewer ecosystem characteristics that have been associated with rat activity. We demonstrate that sewers with narrower pipes, lower flow rates, and construction materials, such as brick and clay, are associated with more rat activity. Further, this review suggests that poorly maintained sewers may contain more crevices and cracks for rats to burrow, leading to greater levels of infestation. Finally, we find that sewers located in residential areas, or closer to food establishment, are more prone to rat presence. Together, these findings uncovered several significant implications for management of rats in sewers, as well as highlight the need for these characteristics to be considered in the urban planning process. Future work is needed to explore how rats in sewers and their management impact above ground populations of rats and other urban wildlife.