Where do Norway rats live? Movement patterns and habitat selection in livestock farms in Argentina

Context The Norway rat (Rattus norvegicus) is recognised as one of the most harmful invasive mammal species in natural, urban and rural environments worldwide. Prevention and control of pest species in livestock farms is necessary to protect animal and human health, but control practices usually do not take into account the biology and ecology of the species to be controlled. The understanding of the biological requirements of Norway rats is necessary for the implementation of efficient management actions. Aims The aim of this research was to study movement patterns and habitat selection of Norway rats on livestock farms in central Argentina. We hypothesised that rats select specific areas within the farms according to the farm’s structure and to the availability of resources. Methods We conducted live-trapping of rats in a pig farm and a dairy farm, during each of four seasons over 1 year. Traps were active for three consecutive days at each trapping session. Movements and habitat selection were assessed by spool-and-line technique combined with environmental surveys and GIS tools. Key results We captured a total of 133 Norway rats and evaluated the movements of 47 individuals. The mean length travelled, registered for one night, was 84.28±38.21m. They did not travel great linear distances within the farms, but instead performed tortuous trajectories around specific sites. Norway rats selected sites containing food, water and refuges; and avoided travelling across areas with short vegetation. Sites containing food sources were most preferred. Conclusions Because food sources for rats were present ad libitum in farms, our findings strongly support the idea that management strategies of prevention and control of this species must include adequate rodent-proof food storage. Also, because rats are found close to livestock, improvement in preventing rats’ access to animal sheds is necessary to prevent contamination of livestock feeders with pathogens carried by rats. Implications The present study provides novel information about the ecology of Norway rats on livestock farms. We encourage farmers to follow our recommendations in order to improve rodent-control strategies.