Home range and movement in populations of Rattus norvegicus polymorphic for warfarin resistance

Movements of brown rats were deduced from records made during a capture-recapture study of rural populations on two farms in Mid-Wales. Populations in the hedges were sampled at monthly intervals for two years, but samples from the farm buildings were obtained only irregularly and by a variety of methods. On the main trap line, of the rats captured during at least two sampling periods 35 (78%) females and 57 (74%) males appeared to have established home ranges, the best estimates of mean home range length for each sex being 54.8 m and 66.1 m respectively. The longest recorded distances travelled during known life were 850 m for a female and 954 m for a male, although the median distances travelled were only 43 m and 52 m respectively. The median distance travelled during a sampling period (seven nights) was about 24 m for both sexes. There were no significant differences between the distances travelled by the sexes or by different age groups, and there was little seasonal variation. Infestations in the hedges were always associated with streams, and those more than about 100 m from the buildings seldom persisted through winter. During autumn and winter the rats in the more distant localities tended to move towards the buildings, but there was no suggestion of an orderly migration. Twenty-seven out of 386 rats marked in the hedges were recovered amongst 576 taken from the buildings, but only nine of diem had travelled more than 100 m. No rats released in the buildings were captured in the hedges. Rats established in the buildings seemed to exclude rats immigrating from the hedges.