Grooming exchange between mothers and non-mothers: the price of natal attraction in wild baboons (Papio anubis)

In a biological market, individuals seek to maximize their benefits by trading social commodities with the partner offering the highest value. When demand for a partner or commodity is greater than supply, individuals compete for access to the preferred partner by raising the price they are willing to pay. In primates, this model has been used to explain the pattern of grooming between mothers of new infants and other individuals who attempt to handle those infants. Here we describe the pattern of interactions with mothers of newborn infants in a group of wild olive baboons (Papio anubis) in Laikipia, Kenya. Females in this group provide a greater share of grooming within bouts when their partners have young infants than when they do not have young infants. Females groom mothers longer when they handle her infant than when they do not. However, females do not compete for access to infants by raising their grooming offers to mothers as the availability of infants declines. The change in relative grooming contributions results from mothers decreasing their grooming rather than non-mothers increasing their contributions. These results suggest that females do trade across currencies, but market pricing does not always explain the pattern of exchange.