Opposing offspring sex ratio variations with increasing age and weight in mouflon mothers (Ovis musimon)

There are two main theories explaining offspring sex biases in polygynous m ammals. Trivers and Willard (1973) argue that mothers with greater reproduc tive resources should invest in the sex with the greater variance in reprod uctive success, usually sons. In contrast, because daughters in many polygy nous mammals stay with their mother and compete with her for food, Local Re source Competition theory (e.g. Clark, 1978; Silk, 1983) predicts that the mothers with the greatest reproductive resources should invest in daughters . We investigated the strategy of sex allocation of a captive, outdoor popu lation of 139 mouflon mothers, Ovis musimon, kept in a game state. A comple x picture emerged in which, despite weight and body condition being correla ted with age in female mouflons, mothers lambed more daughters with increas ing age but also, within a given age, gave birth to more sons with increasi ng weight. Results may be useful in game management aimed at increasing the recruitment or quality of males in managed populations.