Abstract

Sexual selection drives reproductive strategies, particularly in highly polygynous species. In ungulates, a common strategy for securing exclusive access to females during the mating season is the formation of mating groups, consisting of a dominant male, multiple females and a few subordinate males. Defending these groups from rivals while courting females is energetically costly for males, whereas females are choosy and prefer high-quality males. To optimize mating investment, both sexes are expected to adjust their behaviour based on female reproductive status. This study examines how female reproductive status (fertilized vs. unfertilized) influences the mating behaviour of reindeer (Rangifer tarandus). For this purpose, a field experiment was conducted on semi-domesticated reindeer in Finland. We found that males courted unfertilized females significantly more frequently than fertilized ones, whereas female activity budgets did not differ with reproductive status, likely due to activity synchrony within mating groups. Moreover, the proportion of unfertilized females was significantly higher in the core areas of mating groups compared to both mating groups overall and the entire population. Male rank also affected these patterns, with the highest-ranking male courting and remaining close to a higher proportion of unfertilized females than lower-rank males. These findings demonstrate that beyond direct competition, males in polygynous systems exhibit selective courtship behaviours, potentially to increase reproductive success while reducing the cost. Our study highlights the use of spatial strategies by females within mating groups that could help maximize reproductive opportunities with high-ranking males.