Dominance rank, copulatory behaviour and estimated reproductive success in male reindeer

Abstract

Abstract. Relationships between dominance rank, copulatory behaviour and reproductive success within a single mating season were examined in 13 male reindeer, Rangifer tarandus, in a semi-free-ranging population. A linear dominance hierarchy existed only among the top six ranking males. The top-ranking male monopolized access to oestrous females. Frequency of copulation and estimates of reproductive success increased significantly with increasing dominance rank. Reproductive success estimated from 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 three ranking males and the other males were more successful than expected. Mate choice by females and pair interference by males would have skewed reproductive success in favour of higher ranking males. On the other hand, chasing activity and vocal display indicated that male mating efforts were costly. With these behavioural costs and reduced forage intake, high-ranking males eventually became exhausted. The ratio of actual to expected reproductive success of the top-ranking male decreased from 0·98 (11-17 October) to 0·57 (18-24 October). Consequently, mating opportunities for the low-ranking males increased during the second half of the mating season.