Social segregation is not a consequence of habitat segregation in red deerand feral soay sheep

In many sexually dimorphic mammals, adults tend to form single-sex groups ( 'social segregation'). It has been assumed that social segregation is simpl y a by-product of sex differences in habitat use ('habitat segregation'). I tested this assumption on red deer, Cervus elaphus, and feral soay sheep, Ovis aries, using data on group Composition, habitat use and space use coll ected on the Scottish islands of Rum (1974-1993) and Hirta (1985-1994), res pectively. If social segregation had been a by-product of habitat segregati on, then (1) social segregation should have been influenced by the same env ironmental parameters that influence habitat segregation and (2) degree of social segregation should have equalled (and in no case been larger than) d egree of habitat segregation. However, I found that weather parameters that influence habitat segregation did not influence social segregation in red deer and that degree of social segregation was significantly larger than de gree of habitat segregation in both species. I conclude that social segrega tion is not a by-product of habitat segregation in either species, and disc uss the implications of this finding. (C) 1999 The Association for the Stud y of Animal Behaviour.