DOMINANCE RANK, COPULATORY-BEHAVIOR AND ESTIMATED REPRODUCTIVE SUCCESS IN MALE REINDEER

Relationships between dominance rank, copulatory behaviour and reprodu ctive success within a single mating season were examined in 13 male r eindeer, Rangifer tarandus, in a semi-free-ranging population. A linea r dominance hierarchy existed only among the top six ranking males. Th e top-ranking male monopolized access to oestrous females. Frequency o f copulation and estimates of reproductive success increased significa ntly with increasing dominance rank. Reproductive success estimated fr om the frequency of copulation did not differ from that predicted by a priority of access model but it was less than expected for the top th ree ranking males and the other males were more successful than expect ed. Mate choice by females and pair interference by males would have s kewed reproductive success in favour of higher ranking males. On the o ther hand, chasing activity and vocal display indicated that male mati ng efforts were costly. With these behavioural costs and reduced forag e intake, high-ranking males eventually became exhausted. The ratio of actual to expected reproductive success of the top-ranking male decre ased from 0.98 (11-17 October) to 0.57 (18-24 October). Consequently, mating opportunities for the low-ranking males increased during the se cond half of the mating season.