Bachelor groups form due to individual choices or environmental disrupters in African striped mice

International audienceIn several mammal species, bachelor groups occur as a regular life history stage between dispersal and becoming the breeding male of a multi-female group. However, it is rarely investigated how such groups come into existence and how males that choose this strategy differ in life history traits from other males. Males of the socially flexible African striped mouse Rhabdomys pumilio have been historically reported to adopt one of three alternative tactics, i.e., small group-living philopatric males, intermediate solitary living roaming males, or large group-living territorial males. Here, we describe for the first time, bachelors as a fourth male tactic. Using long-term data from 13 generations of striped mice we show that there are in fact two types of bachelor groups: first, kin bachelor groups formed when all females disappeared, probably due to predation; and second non-kin bachelor groups formed by unrelated males that originate from different groups. Whereas kin bachelor groups occurred more frequently during the non-breeding season, non-kin bachelor groups were most common in the breeding season and had a shorter tenure, since most of these males soon switched to the solitary roaming tactic or the territorial breeder tactic. Importantly, we found that non-kin bachelors were heavier and older than kin bachelors and that they did not differ from solitary roaming males in body mass and age. In summary, we identified two different forms of bachelor groups, kin bachelors whose female group members disappeared and larger non-kin bachelor groups showing traits of an alternative reproductive tactic. Both types of bachelor groups differed in multiple traits, demonstrating that it is important to follow the life histories of individuals to understand the mechanisms leading to alternative tactics