GIS-modelling the distribution of Rattus norvegicus in urban areas using non toxic attractive baits

GIS supplies a useful way for analysing and modelling spatial distribution of brown rats Rattus norvegicus in urban areas, supplying maps that predict the occurrence of rats over larger areas. However, two alternative procedures can be used: landscape-based models, which use habitat variables derived from remote sensing satellites or other thematic maps, and interpolation techniques, which convert point samples of species abundance. The first procedure has been previously applied, while the second has never been used until now. In this study, we valued the effectiveness of the interpolating procedure by modelling the distribution of brown rats in a large urban area of northern Italy. During spring and autumn 2004, we positioned non toxic baits in 119 spots distributed over the whole urbanized area of the city and we generated maps of rat presence/absence for the two seasons. Brown rats were irregularly scattered over the city and concentrated mainly around rivers and ditches, as well in the historic centre, particularly where buildings suffer poor maintenance. Seasonal variation of rat occurrence was also detected. Brown rat occurrence may be reliably predicted by the interpolation procedure, which appeared to be a more efficient approach to rat distribution modelling compared with landscape-based procedures.