In large mammalian herbivores, the increase of group size with habitat openness was first assumed to be an adaptive response, encoded in the individual. However, it could, alternatively, be an emergent property: if groups were nonpermanent units, often fusing and splitting up, then any increase of the distance at which animals perceive one another could increase the rate of group fusion and thus mean group size. Dynamical models and empirical data support this second hypothesis. This is not to say that adaptive modifications of mean herd size cannot occur. However, this changes the way in which we can envisage the history of gregariousness in large herbivores during the Tertiary.

The purpose of this study was to see if mouflon (Ovis gmelini) females with lambs have feeding habitats similar to other sex‐age classes in spring, in an area without large natural predators. Parous ewes restricted themselves to rocky and poor nutritive habitats but lambed within their winter home range. Once in matriarchal groups, females with lambs ≥ three days old fed more on rocky areas and stayed closer to safe terrain than did other mouflons which more frequently used slope tops, patches containing herbs, and pastures around a little village. Segregation between the two categories of mouflons was reduced when lambs were several weeks old during the peak growing season. Seclusion of parous females may be explained by potential predation by foxes on neonates, an asocial tendency, the need to form mother‐young bonds and the necessity for the young to develop locomotor skills. Rocky areas may also provide favourable microclimatic conditions. Two non‐exclusive hypotheses may account for the tendency of lactating females to remain near ‘escape’ terrain. First, the anti‐predator strategy could be driven in the absence of predators because of phylogenetic inertia. Secondly, the anti‐predator strategy may be learned during the autumn hunting season and exhibited during the lambing season even without predation.

Sexual segregation reported in many wild ruminants is generally assumed to result from either different habitat choices by adult males and females or`social factors'. In this framework, we studied group composition and habitat use of mou¯on sheep (Ovis gmelini) over an annual cycle in the low-mountain range of Caroux-Espinouse (continental France). The analysis of group composition revealed segregation outside the rut, not only between the sexes, but also between the young (2±3 years) and old rams (! 4 years). Moreover, ewes, young rams, and old rams exhibited some differences in patterns of habitat use in the mid-rutting and lambing seasons, but showed similar patterns in winter and summer. These results, juxtaposed with those of studies of interactions and proximity between individuals within groups, suggest that segregation between age-sex classes has a strong social basis in mou¯on sheep.

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