High early lactational synchrony within baboon groups predicts increased infant mortality

Abstract

Female-female competition may be particularly acute when many females in the same social group have dependent young at the same time, with potential negative consequences for offspring survival. Here, we used more than four decades of data on wild baboons (Papio sp.) in Amboseli, Kenya, to examine the effects of early lactational synchrony (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 early lactational synchrony to intensify both female-female aggression and maternal association with males, who can buffer infants from conspecific harassment. In support of these predictions, when early lactational synchrony was high, new mothers initiated more agonistic contests. Further, high-ranking females increased their time associating with adult males, which may limit the ability of low-ranking females to receive male protective services and may have downstream consequences for female foraging efficiency. Finally, high early lactational synchrony 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 alters competitive regimes and compromises reproductive outcomes even in nonseasonal breeders.