Since the 1970s animal scientists have described species in which the sexes compete over how sperm is used. Birkhead is author of several books that describe different approaches to sperm competition in animal species. In some varieties of birds, for example, males physically manipulate the female before or after copulation to increase the odds of fatherhood. More impressive are females who can store and manipulate the sperm of many males in their reproductive organs. Discovering the mechanisms of sperm competition is not easy, and most studies have focused on males.
Females can be incredibly subtle.
Only recently have we begun to discover the sophisticated mechanisms that females have evolved to counter male sexual behavior. The results of this study appear in the current issue of Nature . For a sexually harassed female, sperm ejection was the last resort. A hen would first try to run away. If caught, she would then issue a call for help to the dominant male, who sometimes would chase away the aggressor.