Differential Reproduction Among Red Deer (Cervus elaphus) Stags on Rhum

(1) Variation in male reproductive success in red deer is analysed using 5 years' data from the Isle of Rhum (Scotland). The existence of lifetime reproductive differentials is inferred from the following results. (2) Estimates of numbers of calves sired (calculated from data on social grouping during the mating season and subsequent calving times) showed large differences in reproductive success between different adult stags (over 4 years old) within seasons. Younger animals were unlikely to mate. (3) Variation in reproductive success among adults was not primarily age-dependent. (4) The magnitude of consistent individual differences in reproductive success over successive seasons makes the equalization of lifetime success by differential mortality improbable. Mortality might be raised in successful breeders because, as suggested by a correlation between reproductive success and antler casting time (an index of winter body condition), energy expenditure may increase with reproductive success.