Timing of Reproductive Effort Differs between Young and Old Dominant Male Reindeer

Abstract

In polygynous species, male reproductive effort has been measured both directly in the form of somatic costs and indirectly using behavioral data. We used 12 years of data collected from a semi-domesticated reindeer population in northern Finland to investigate age- and time-specific patterns of dominant males' reproductive effort. Overall, we found that activity levels differed both between young and old dominant reindeer males, and among the early, peak, and late rut, the pattern being age-specific. Reproductive effort was generally higher for old than young dominant males; however, old males reduced their effort in the late-rut period, while young males maintained the same level of activity. There was a positive relationship between somatic costs and activity level only during the early rut for young dominant males, and only during the peak rut for old dominant males. Thus, old males incur the highest energetic costs from rut-related activities when most of the females in the herd are in oestrus. Conve...