Women who have beaten the odds to find themselves in the upper echelons of science face a further hurdle—visibility. Female scientists are less likely to sit on science advisory boards, receive awards, and give invited talks at conferences. However, a new study suggests that the reasons women appear less often on the podium are complicated.

Reporting in the Journal of Evolutionary Biology, Julia Schroeder of the Max Planck Institute for Ornithology in Germany and Hannah Dugdale of the University of Sheffield in the United Kingdom found that only 16% of invited speakers at the European Society for Evolutionary Biology Congress between 2001 and 2011 were women. The total—66 of 430 individuals—was half of what would be expected based on the number of senior female scientists in the life sciences.

The dearth of women is not because they aren't being invited. Instead, female scientists were twice as likely as their male counterparts to turn down an invitation to talk in slots reserved for presenting original and important work. At the same time, the number of female presenters of posters and uninvited talks was almost at parity with men.

Evolutionary biologist Trudy MacKay of North Carolina State University in Raleigh says that relatively short notice and a tight budget contributed to her decision to decline an invitation to talk at the congress in 2011. Women also turn down talks because they receive too many invitations each year and are anxious about balancing the demands of family and work, says Jeanine Olsen of the University of Groningen in the Netherlands, who headed one of Europe's Seventh Framework Programme's Gender Action Plans aimed at promoting gender awareness. Younger women also tend to do less self-promotion, Olsen adds.

Finding ways to address those issues is next on Schroeder and Dugdale's agenda. And the first step is to contact scientists to find out why they declined invitations. "Then we [will] know what can be done to change their minds," Schroeder says.