Social organization of reindeer (Rangifer tarandus), with special reference to relationships among females

Approximately 130 individually recognized reindeer, plus unidentified calves, were observed over the course of 9 months from the rutting period to the calving period in Finnish Lapland. The level of association among nonrelated females in resting groups fluctuated with the passage of time. Among related females, only yearling daughters associated significantly with their respective mothers, although coexistence between mothers and yearling daughters was accompanied by antagonism. Two-year-old daughters were next in terms of association with their mothers, whereas daughters of 3 years of age and older rarely associated with their mothers and the level of association decreased to the level observed for nonrelated females. When two herds joined each other, the frequency of antagonistic interactions among foreign individuals was initially quite high. Thereafter, the two herds became united as a new herd within a week or two. A linear dominance hierarchy was found among 90 females that joined the studied herd. Their social rank was correlated with body weight. Thereby, the dominance hierarchy was stably maintained even though the herd itself was a temporary association of individuals. During the nonrutting period, animals segregated themselves by sex. The shedding of male antlers was correlated with drastic changes in ranking.