Vigilance costs of allogrooming in macaque mothers.

Although primate allogrooming is a time- and energy-consuming activity, it has never been demonstrated clearly to have any reproductive costs. In this study, I tested the hypothesis that allogrooming may have reproductive costs to the performer in that it may reduce its vigilance behavior. Subjects of the study were 15 mother-infant rhesus monkey dyads belonging to four captive groups. Data were collected over the first 12 wks of lactation. When mothers groomed other individuals and their infants were away from them, maternal glance rate at the infant was markedly reduced, and infants were victims of harassment and aggression by other group members at a higher rate than during nongrooming time. In spite of a higher risk of harassment of infants, mothers did not try to minimize allogrooming time when infants were away. It is argued that, under natural conditions, the reduced vigilance associated with allogrooming may also expose an individual and its offspring to an increased risk of predation.