SOCIAL-STRUCTURE IN SYNANTHROPIC POPULATIONS OF A MURID RODENT MASTOMYS-NATALENSIS IN SENEGAL

Synanthropic populations of Mastomys natalensis (A. Smith, 1834) were studied in southeastern Senegal in order to evaluate some elements of their social structure. Analysis of trapping data consisting in single and multiple captures indicates that adult males were less likely to be involved in multiple captures than any other category of individual s. Sex-ratio in adults was significantly female-biased, and multiple c aptures involving 4 individuals or more (up to 13) were characterized by the small number of adult males involved (usually one per capture). Dyadic encounters between males revealed a higher rate of aggressive behaviours in M. natalensis than in its sibling species M. huberti. Th ese observations suggest that these synanthropic populations are subdi vided in polygynous units in which: (1) a part of males are evicted fr om the social group before their maturity and (2) adult males of diffe rent social units display aggressive behaviour towards each other.