Sex-specific differences in reindeer calf behavior and predation vulnerability

According to reproductive strategy theory, males in polygamous breeding systems should invest in morphological or behavioral features that increase reproductive success. When the early development of such traits conflicts with predator protection, we expect that male calves will exhibit risk-taking behavior, such as high activity level and increasing distance from mother, to a greater extent than female calves. We investigated sex differences in mother–calf distance, calf activity levels, and calf mortality in a semi-domesticated reindeer (Rangifer tarandus) population. The results show that male calves stray farther away from their mothers, exhibit a higher level of locomotive behavior in terms of play and walking, and are more vulnerable to predation than are female calves. Although mother–calf distance increased over time in 1- to 6-month-old calves, no evidence was apparent for an increase in sex difference in mother–calf distance over this period. The results suggest a trade-off between predation vul-nerability and investments in behavioral traits thought to be important for future reproductive success and suggest that these sex-related differences in behavior are apparent as early as 6 months of age. Key words: Rangifer tarandus, reindeer, calf behavior, sex differences, sexual segregation, predator vulnerability. [Behav Ecol 14:10–15 (2003)] Reproductive strategy theory assumes that morphologicaland behavioral features that increase reproductive suc-cess are likely to spread in a population (Clutton-Brock et al., 1982). In polygamous ungulates the development of large body size, fighting abilities, and consequent high social statu