Male harassment influences female movements and associations in Grevy's zebra (Equus grevyi)

In traditional models for social organization, female movementsand association patterns track resource distribution, whereasmales track females. More recently, this model has been expandedto include feedback effects of male behavior, especially sexualharassment, on female decisions. In Grevy's zebra (Equus grevyi),males defend territories containing resources attractive tofemales, who form unstable groups. Past research has explainedfemale behavior based on resource distribution and needs alone.Lactating females have been found to have restricted movementsand fewer male associates than nonlactating females, a patternwe find in our study. This pattern has previously been attributedsolely to the higher water needs of lactation. However, in ourpopulation, both lactating and nonlactating females are typicallyclose to water. We test the hypothesis that male harassmentalso influences female ranging and associations with males.This effect is predicted to be greater for lactating femalesbecause harassment has higher costs to them. We find that lactatingfemales experience higher harassment rates than those of nonlactatingfemales. Lactating females tend to move faster during harassmentperiods, whereas nonlactating individuals do not. Lactatingfemales experience lower harassment rates if they spend moretime with a particular male, whereas nonlactating females' harassmentrates do not depend on their allocation of time to a primarymale. We suggest that females concentrate their time with onemale in order to reduce male harassment. Even in species suchas Grevy's zebra without strong male–female bonds, socialinteractions may be a significant driver of female distribution.