The presence and number of male competitor's scent marks and female reproductive state affect the response of male meadow voles to female conspecifics' odours

Male mammals are attracted to the scent marks of sexually receptive female conspecifics. Male voles spend more time investigating the scent marks of female voles in postpartum oestrus (PPE), a heightened state of sexual receptivity that occurs following the delivery of a litter, compared to those of female voles that are not in PPE, but in a moderate state of sexual receptivity. However, both types of females will attract male conspecifics to deposit their scent marks near those deposited by these females. The scent marks deposited by these males may indicate how many males have visited this female, which may affect how attractive she is to other males. In the present study, we exposed male meadow voles, Microtus pennsylvanicus, to the scent mark of a PPE female and a female that was not in PPE, a reference female (REF female); the scent marks of 0, 1 or 5 males were placed adjacent to the scent marks of these two female scent donors. In doing so, we tested three hypotheses. The first hypothesis is males will spend less time investigating the scent mark of a female that has more scent marks of male conspecifics adjacent to it compared to that of a female that has fewer scent marks of male conspecifics adjacent to it. The second hypothesis is the converse of the first hypothesis. The third hypothesis is males will spend more time investigating the scent mark of a PPE female than that of a REF female, independent of the number of scent marks of other males adjacent to them. Overall, our data suggests that a combination of factors may influence a male's preference for the scent marks of potential mates. Most tests suggest that males will respond preferentially to a female if she has more male suitors than another female, independent of the reproductive state of either female. If however, the number of male suitors is the same for each female, males tend to prefer the scent mark of the female that is in a more heightened state of sexual receptivity.