Individual differences in spatial utilization of a river-system by otters Lutra lutra

One female and 2 male otters Lutra lutra (Linnaeus, 1758) were radio-tracked in the River Don catchment, Aberdeenshire, Scotland, between April 1988 and June 1990, and their range use patterns were compared. The males had longer total ranges than the female. The range of the larger male almost completely overlapped with that of the female, but the range of the smaller male was mainly separate from that of the female. The ranges of the 2 males only partially overlapped, with the larger male having the greatest total range, nightly range and rate of travel, and the lowest tendency to revisit areas during the night. The smaller male was relatively sedentary, using two separate core areas, whereas the other 2 otters had single core areas and frequently patrolled their total ranges. As the larger male was sexually active, but the smaller one did not appear to be, it was argued that the need to search for mates could explain some of these differences in spatial patterns. All 3 otters used tributaries more than expected based on the areas within their total ranges. This may be because riparian margins were used in greater proportion than central areas of the channel width.