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-t racked in the River Don catchment, Aberdeenshire, Scotland, between Ap ril 1988 and June 1990, and their range use patterns were compared. Th e males had longer total ranges than the female. The range of the larg er 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 small er male was relatively sedentary, using two separate core areas, where as the other 2 otters had single core areas and frequently patrolled t heir total ranges. As the larger male was sexually active, but the sma ller one did not appear to be, it was argued that the need to search f or mates could explain some of these differences in spatial patterns. All 3 otters used tributaries more than expected based on the areas wi thin their total ranges. This may be because riparian margins were use d in greater proportion than central areas of the channel width.