Rank Acquisition Through Birth Order in Mouflon Sheep (Ovis gmelini) Ewes


Colette Guilhem Institut de Recherche sur les Grands Mammifères, INRA, BP27, F–31326 Castanet-Tolosan, France. E-mail: colette.guilhem@caramail.com


The relationship between mothers’ and daughters’ dominance ranks was studied in a captive herd of mouflon sheep (Ovis gmelini), including nine adult ewes and their daughters, observed as lambs and yearlings. We found a positive correlation between the ranks of mothers and those of their yearling daughters, even though every mother dominated all the yearlings. We then tested the hypothesis that daughters from subordinate ewes became subordinate within their own age class because, as lambs, they had received more aggression from the other ewes in the herd. Recorded data were inconsistent with the hypothesis, even showing a trend for female lambs to receive aggression more frequently when born from dominant ewes. We also tested the hypothesis that resemblance between mothers’ and daughters’ ranks was due to inheritance of aggressiveness. No significant correlation was found between mothers’ and daughters’ aggressiveness, so the hypothesis was not supported. Finally, we found a significant concordance between mothers’ ranks, daughters’ ranks, and daughters’ birth dates. Earlier-born daughters became dominant over later-born ones, probably because of larger body size and more advanced social behaviour. The age of most of the mothers was undetermined, but in mouflon sheep, older ewes generally dominate younger ewes and are known to lamb earlier during the birth season. Accordingly, it is suggested that dominant ewes have daughters dominant in their own age class, because (1) age influences the parturition date during the birth season, and (2) age strongly influences rank, even in individuals born during the same lambing season.