Temporal distribution and weather correlates of Norway rat (Rattus norvegicus) infestations in the city of Madrid, Spain

Urban Norway rats are challenging pests, posing significant health and economic threats. Implementing ecologically based integrated rodent management (EBIRM) programmes relies primarily on the understanding of ecological relationships between rodents and their environments, with emphasis on the processes influencing rodent populations in the target ecosystem. We investigated the temporal distribution of urban Norway rat infestations in Madrid, Spain, and tested for the association of such infestations with temperature, relative humidity and precipitation by fitting a multivariate Poisson generalized linear model to a 3-year (2006-2008) daily time series of 4,689 Norway rat sightings. Norway rat infestations showed a marked seasonality, peaking in the summer. Most Norway rat sightings were reported on Mondays. Minimum temperature and relative humidity were positively associated with Norway rat infestation, whereas the association with precipitation was negative. The time series was adequately explained by the model. We identified previously unrecognized time periods that are more prone to Norway rat infestation than others and generated hypotheses about the association between weather, human outdoor activity, resource availability, rodent activity and population size. This provided local authorities engaged in preserving urban ecosystem health with basic research information to predict future rodent outbreaks and support the implementation of EBIRM programmes in urban areas.