Social segregation is not a consequence of habitat segregation in red deer and 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 simply 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 collected on the Scottish islands of Rum (1974-1993) and Hirta (1985-1994), respectively. If social segregation had been a by-product of habitat segregation, then (1) social segregation should have been influenced by the same environmental parameters that influence habitat segregation and (2) degree of social segregation should have equalled (and in no case been larger than) degree 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 degree of habitat segregation in both species. I conclude that social segregation is not a by-product of habitat segregation in either species, and discuss the implications of this finding. (C) 1999 The Association for the Study of Animal Behaviour.