In sexually dimorphic ungulates, male reproductive success depends on fighting with other males for access to females during a brief rutting season. Large body size is necessary for success in intrasexual competition, and a few large-sized males are often able to monopolize access to female groups. Earlier studies have reported that reproductive effort increases with age until prime-age is reached, and one study that population density lowered effort in (older) males. No study has directly assessed whether there is within-age-class variation in effort resulting from varying levels of intra-male competition. It is reported here the weight loss during the rutting season of 54 individual male reindeer Rangifer tarandus coming from eight herds with varying density (3.3–6.0 deer/km2) and sex ratio (4–28% males). In agreement with earlier studies, reproductive effort was lower for young (1- to 2-year-old) than for prime-aged (3- to 5-year-old) males both on an absolute and relative scale. Among 1-year-old males (n=33), effort was lower as sex ratio became closer to even, but density during the rutting season had no effect. This suggests that yearling males take a more active role when prime-aged males are absent. In addition to the insight into male ungulate life history, understanding male rutting behaviour may also have implications for population dynamics.