Predictors and consequences of gestation length in wild chimpanzees

Objectives Energetics are widely recognized to influence timing of birth in humans and other eutherian mammals, yet considerable variation exists in the relationship between energetic constraints and gestation length. In humans, poor nutrition and short inter‐gestational intervals (IGIs) are associated with shorter gestations. In other mammals, lower energy availability is usually associated with longer gestations. We investigated the predictors of gestation length, and the impact of gestation length on offspring survival, in chimpanzees, humans' closest living relatives. Materials and Methods We used 50 years of demographic and behavioral data to estimate gestation lengths in the wild chimpanzees of Gombe National Park, Tanzania, and then used ecological and demographic data to explore the predictors and consequences of gestation length in our sample. Results Gestation lengths were shorter for females in their early 30s (relative to younger and older females), and after short IGIs. Other predictors potentially associated with maternal energetic condition and maternal investment were not associated with gestation length. We also found that shorter gestation lengths corresponded to lower offspring survival. Discussion Like humans, chimpanzees had shorter gestations after short IGIs, and short gestations were associated with higher offspring mortality. We consider competing explanations for the conflicting relationships between energetics and gestation length across eutherian mammals in light of these results.