Highly Competitive Reindeer Males Control Female Behavior during the Rut

During the rut, female ungulates move among harems or territories, either to sample mates or to avoid harassment. Females may be herded by a male, may stay with a preferred male, or aggregate near a dominant male to avoid harassment from other males. In fission-fusion group dynamics, female movement is best described by the group’s fission probability, instead of inter-harem movement. In this study, we tested whether male herding ability, female mate choice or harassment avoidance influence fission probability. We recorded group dynamics in a herd of reindeer Rangifer tarandus equipped with GPS collars with activity sensors. We found no evidence that the harassment level in the group affected fission probability, or that females sought high rank (i.e. highly competitive and hence successful) males. However, the behavior of high ranked males decreased fission probability. Male herding activity was synchronous with the decrease of fission probability observed during the rut. We concluded that male herding behavior stabilized groups, thereby increasing average group size and consequently the opportunity for sexual selection.

在发情期，雌性有蹄类动物会在不同配偶群或领地间移动，或为评估潜在配偶，或为躲避雄性骚扰。雌性可能被雄性驱赶、与偏好的雄性个体共处，或是聚集在优势雄性附近以规避其他雄性的骚扰。在裂变-融合群体动态（fission-fusion group dynamics）中，雌性的移动模式最佳表征方式为群体的裂变概率，而非跨配偶群移动。本研究旨在检验雄性驱赶能力、雌性配偶选择或骚扰规避行为是否会对群体裂变概率产生影响。我们对佩戴带活动传感器的GPS项圈的驯鹿（Rangifer tarandus）种群的群体动态进行了记录。研究结果显示，并无证据表明群体内的骚扰水平会影响裂变概率，亦未发现雌性会主动寻求高地位（即竞争能力强且繁殖成功）的雄性个体。然而，高地位雄性的行为会降低群体裂变概率。雄性的驱赶行为与发情期内观察到的群体裂变概率下降同步发生。我们据此得出结论：雄性的驱赶行为可稳定群体结构，进而提升平均群体规模，最终为性选择提供更多机会。