High early lactational synchrony within baboon groups predicts increased female-female competition and infant mortality

Abstract

Female-female competition may be particularly acute when many females in the same group have dependent young simultaneously, with potential negative consequences for offspring survival. Here, we used 45 years of data on wild baboons (Papio sp.) in Amboseli, Kenya, to examine the effects of early lactational synchrony (ELS, the proportion of females in a group with an infant <90 days old) on female-female agonistic interactions and infant survival. Because early lactation is energetically demanding for mothers and high-risk for infants, we expected ELS to intensify both female-female aggression and maternal association with males, who can buffer infants from conspecific harassment. In support, when ELS was high, new mothers initiated more agonistic contests. Further, high-ranking females increased their time associating with males, which may limit the ability of low-ranking females to access to male protective services. Finally, high ELS strongly predicted infant mortality. This association may result from both aggression among adult females and infanticidal behavior by peripubertal females. Our findings provide evidence that synchronous reproduction can alter competitive regimes and compromise reproductive outcomes even in nonseasonal breeders.