A long-term study of Rattus norvegicus in the London borough of Enfield using baiting returns as an indicator of sewer population levels.

This is a long-term study that investigates the dynamics of a population of Rattus norvegicus (Berk) inhabiting a sewerage system in London. Thirteen years (1986/7-1998/9) of data from sewer baiting records were analysed (a total of 35,478 records). Manholes were baited with the anticoagulant Brodifacoum (0.005%) on a pinhead oatmeal bait base. Time series analysis was conducted on the data set to determine the underlying trend of the data and the population fluctuations about this trend. An exponential curve was found to give an accurate and realistic fit to the data and indicated that the rat population had decreased over the study period. Decomposition analysis indicated a 5-year cycle best described fluctuations around this trend.