Importance of group dynamics on female mating behaviour in reindeer Rangifer tarandus

The aim of this work is to investigate female mating behaviour in reindeer Rangifer tarandus using a combination of both field and GPS based data. By developing adequate methodology, I was able to remotely estimate individual activity budgets, and to investigate fission-fusion group dynamics in a controlled herd. Variations of the group dynamics revealed an increase in group size at the beginning of the peak rut, resulting from an increase of group cohesiveness. I demonstrated that this increase in cohesiveness resulted from the herding behaviour of males, rather than female mate choice. Harassment avoidance marginally increased the group cohesiveness, as females may have preferred to remain within the group to avoid the costly solitary situation where they were harassed by low quality males during the peak rut. However, forming larger groups appeared to be costly, since increasing group size increased the disturbance level on female activities due to foraging competition. Therefore, I rejected the hypothesis of harassment dilution, which states that females aggregate to decrease the per capita level of harassment. Instead, a trade-off appeared on female mating tactic between foraging competition and harassment avoidance; between a large group dominated by an adult male, and a small group dominated by a young harassing male. By demonstrating that a proximate process (males herding females) was responsible for the pattern at the population level (the increase of the average group size), I validated the self-organization theory on ungulate group dynamics. I also used these semi-experimental conditions to correct and validate a field-based measure of the intensity of the group dynamics