Dead-infant carrying by chimpanzee mothers in the Budongo Forest

Abstract

It has been suggested that non-human primates can respond to deceased conspecifics in ways that suggest they experience psychological states not unlike humans, some of which could indicate they exhibit a notion of death. Here, we report long-term demographic data from two East African chimpanzee groups. During a combined 40-year observation period, we recorded 191 births of which 68 died in infancy, mostly within the first year. We documented the post-mortem behaviour of the mothers and describe nine occasions where Budongo chimpanzee mothers carried infants for 1-3 days after their death, usually until the body started to decompose. We also observed three additional cases of extended carrying lasting for more than 2 weeks, one of which was followed by the unusual extended carrying of an object and another which lasted 3 months. In each case, the corpses mummified. In addition, we report four instances of recurring dead-infant carrying by mothers, three of whom carried the corpse for longer during the second instance. We discuss these observations in view of functional hypotheses of dead-infant carrying in primates and the potential proximate mechanisms involved in this behaviour.

Keywords: Death; Infant corpse carrying; Pan troglodytes; Thanatology.

Fig. 1

Dead-infant carrying occurrences for each mother–infant pair relative to the average daily rainfall (data extracted from Budongo Conservation Field Station long-term records 1993–2018). Single red dots represent occurrences of carrying that lasted between 1 and 3 days. Red dots connected with a line represent the approximated duration of extended carrying, with the dots representing the start and end of carrying

Fig. 2

KET holding KYO’s mummified body while sitting on a tree (picture taken by A.S. on 21 January 2018)

Fig. 3

UP carrying UP4’s mummified body in her hand while travelling on the ground (picture taken by E.F. on 30 August 2021)