Behaviorally Solitary and Spatially Grouped
Previously described as strictly solitary, in my earlier work in the Laikipia District of Kenya, we discovered that striped hyenas form small, stable spatial groups of up to three adult males and a single reproductively mature female. Individual home-ranges (HRs) for hyenas in the three main spatial groups on the primary Loisaba study site from 1999 thru 2003 are illustrated below. Note that the two females in the eastern group were successive, not contemporary, residents and the male with the small (purple) HR in the south was a short-term resident.
Although spatial group members shared ranges and occasionally rested together, striped hyenas always foraged alone. Superficially, the social system of the striped hyena appears similar to other carnivores that form male coalitions. However, it is only in the striped hyena that we find multi-male, single female use of common, exclusive ranges within which several males share a single female. Nevertheless, conventional explanations for group formation and social evolution have probably correctly identified the influential factors at work (e.g. abundance and dispersion of food and mates,as resources). However, the interaction between those factors has resulted in unexpected patterns of association in this species. Solitary female distributions likely reflect a lack of permissive and promoting conditions for group formation (e.g. uniformly distributed and small prey items comprising a substantial proportion of diet). However, by the same logic, we would expect males to be solitary in response to overdispersion of females (and food). Instead, the monopolization of single females by multiple males may reflect an additional trade-off between the cost(s) of sharing a female and the benefits of cooperative and effective defense of that female against a greater number of neighboring males.