The response of male meadow voles, Microtus pennsylvanicus, to same- and mixed-sex over-marks depends on the reproductive state of the topand bottom-female scent donors

Many female terrestrial mammals undergo postpartum estrus (PPE), a state of heightened sexual attractiveness to male conspecifics relative to females not in PPE (REF females). PPE and REF females of several species may use over-marks to maintain territories and attract and indicate interest in males as potential mates. In our first two experiments, we determined if the response of male meadow voles, Microtus pennsylvanicus, to the top- and bottom-scent donors of a samesex over-mark was affected by the reproductive state of the scent donors. We found that after exposure to a same-sex over-mark in which the female scent donors were in the same reproductive state, males spent more time investigating the mark of the top-scent female. Males, however, spent more time investigating the mark of the PPE female to that of a female not in PPE, independent of the position of either female's scent mark in the over-mark. The third and fourth experiments determined if the response of males to the female scent donor of a mixed-sex over-mark was affected by whether she is the top- or bottom-scent donor. In three of the four comparisons, males spent more time investigating the mark of a novel PPE female (not in the over-mark) to that of the top- or bottom-scent female. In addition, males spent similar amounts of time investigating the mark of a novel female not in PPE and that of a top-scent PPE female. However, males spent more time investigating the novel REF female's mark compared to that of a bottom-scent PPE female. The results are discussed in terms of the natural history and mating strategies of male meadow voles.