Thursday May 01, 2008
Scientists say they found this out when they recorded women counting from one to 10 at different times during the month and played the voices back randomly to a group of students.
Both men and women picked voices which had been recorded when the women were at their most fertile.
Conversely, women's voices recorded during non-fertile periods were rated much lower on the scale.
"The results are in line with evidence that the female voice box, or larynx, is under the influence of sex hormones," said a report in the New Scientist.
One of the scientists, Dr Martie Haselton: "We have found that voices are higher in pitch on high-fertility days of the cycle."
The study was carried out
by Dr Gordon Gallup and Nathan Pipitone at the State
University of New York at
Its findings add weight to the theory that women, like animals, experience a form of "oestrus", or being "in heat" although the effects in human are more subtle.
A report last year suggested that lap dancers earned more tips during their fertility days. "The voice changes might explain some of the shift in lap dancer tip earnings," said Dr Geoffrey Miller.
"Dancers certainly chat with their customers."
He pointed out that visual attractiveness also appeared to change during the menstrual cycle. "Voice quality is unlikely to be the whole story," he said.
Dr Gallup suggests that men have learned to pick up on barely perceptible changes in the voices of women which signal that they are fertile.
Other women also notice the effect, possibly to keep a watchful eye on the competition.