Responses of mountain gorillas (Gorilla beringei beringei) to deceased infants.

Studying nonhuman primates' responses to the death of conspecifics has gained growing interest in comparative thanatology providing wider evolutionary context for our understanding of human responses to death and mourning. Primates exhibit diverse reactions to infant deaths, with infant corpse carrying (ICC) being most frequently reported. We tested existing hypotheses about the functional significance of ICC and describe other behaviors directed towards corpses using 21.7 years of observations on mountain gorillas involving 141 infant deaths. ICC is common in mountain gorilla mothers (60.5% of deaths) with an average duration of 4.9 days. Consistent with primate literature, ICC by mothers occurred less often and for shorter durations after traumatic deaths and with increasing infant age at death. Mothers' parity, season, and whether a mother had previously carried an infant corpse did not affect ICC. Non-mothers across age classes and sexes participated in ICC and directed affiliative and investigative behaviors toward corpses, reflecting the important role that non-mother caregivers can play in infant gorillas' development and survival. Nulliparous and primiparous females were proportionally more often non-mother carriers than multiparous females which supports the 'learning to mother' hypothesis. Our findings suggest that delays in overcoming strong attachment bonds and difficulties in detecting death lead to a greater likelihood and longer duration of carrying after death. Understanding these behaviors in mountain gorillas enriches our knowledge of their social and care systems and contributes to broader discussions on primate cognition and responses to death.