In a study published in Evolution and Human Behaviour, Gordon Gallup and Nathan Pipitone from the State University of New York at Albany describe how they recorded women counting up to ten on four different stages during their menstrual cycles. When the recordings were played to a second group of men and women, both the males and the females judged the recordings made when the women were at their most fertile - around day 14 or mid-cycle, to sound more attractive than recordings made at other times of the month.
Gordon Gallup puts this down to the effects of hormones on the voice box, suggesting that it's an example of a woman advertising her fertility.
So why should other women also notice the effect, if the aim is to attract a man? To identify the competition, apparently!
The findings also agree with research carried out by others including UCLA's Martie Haselton who has found that the pitch of the voice increases on high-fertility days, and Geoffrey Miller from the University of New Mexico, who found last year that lap-dancers earn more in tips when they're most fertile.
Together the findings suggest that the female human oestrus is alive and kicking, despite claims by evolutionary biologists in the 50s that humans are far too sophisticated to go around advertising their fertility...