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.

Mother-infant relationships in wild Guinea baboons (Papio papio)

“…The duration of interactions towards the infants in this study (<1 to 5 days) was in line with the reports in other species (e.g., Northern muriquis: 1-3 days [Freire Filho et al, 2022], chacma baboons: 2-10 days [Carter et al, 2020], Japanese macaques: mean 3.3 days (range, 1-17; SD, 2.7) [Sugiyama et al, 2009], Sichuan snub-nosed monkeys: 5 days [Yang et al, 2022]), but relatively short compared to the maximum registered in other primate species (e.g., Tonquean macaques: 25 days [De Marco et al, 2018], Hanuman langurs: 27 days [Sharma et al, 2011], geladas: 48 days [Fashing et al, 2011], chimpanzees: 68 days [Biro et al, 2010] and 89 days [Soldati et al, 2022]). In a similar study with chacma baboons, Carter and colleagues (2020) proposed that the cost derived from carrying a dead infant in species that travel long daily distances leads to short durations.…”

“…In Old World monkeys, such observations include yellow baboons (Papio cynocephalus [Altmann, 1980]), chacma baboons (Papio ursinus [Carter et al, 2020]), Japanese macaques (Macaca fuscata [Sugiyama et al, 2009;Takeshita et al, 2020]), Sichuan snub-nosed monkeys (Rhinopithecus roxellana [Yang et al, 2022]), Indian langurs (Presbytis entellus [Jay, 1962]), Hanuman langurs (Semnopithecus entellus [Sharma et al, 2011]), Geladas (Theropithecus gelada [Fashing et al, 2011]), Zanzibar red colobus (Piliocolobus kirkii [Georgiev et al, 2019]), bonnet macaques (Macaca radiata [Das et al, 2019]), and lion-tailed macaques (Macaca silenus [Das et al, 2019]); in New World monkeys, these species include blonde capuchins (Sapajus flavius [Andrade et al, 2020]), brown capuchins (Sapajus apella [Trapanese et al, 2020]), and northern muriquis (Brachyteles hypoxanthus [Freire Filho et al, 2022]). Post-mortem behaviours have also been observed in several ape species: chimpanzees (Pan troglodytes [Biro et al, 2010;Cronin et al, 2011;Matsuzawa, 1997;Soldati et al, 2022;Van Lawick-Goodall, 1968]), Sumatran orang-utans (Pongo abelii [Dellatore et al, 2009]) and gorillas (Gorilla beringei [Warren & Williamson, 2004]). In these studies, mothers' most frequently observed responses have been care-taking behaviours directed towards their dead infants, such as inspection, protection, and grooming.…”

“…or "do animals grieve?" are central to the discipline of comparative thanatology (Anderson, 2011(Anderson, , 2016Anderson et al, 2018;Bearzi et al, 2018;Carter et al, 2020;Fashing et al, 2011;Fernández-Fueyo et al, 2021;Gonçalves & Biro, 2018;Gonçalves & Carvalho, 2019;Soldati et al, 2022;Watson & Matsuzawa, 2018;Yang et al, 2022).…”

“…The most prominent post-mortem behaviour in nonhuman primates is dead infant carrying (e.g., chimpanzees [Biro et al, 2010;Soldati et al, 2022], gorillas [Masi, 2020;Warren & Williamson, 2004], Japanese macaques [Sugiyama et al, 2009], bonnet and lion-tailed macaques [Das et al, 2019], chacma baboons [Carter et al, 2020], and others (reviewed in Fernández-Fueyo et al, 2021;Gonçalves & Carvalho, 2019;Watson & Matsuzawa, 2018). Whereas some mothers abandon their deceased infants soon after they die, others continue interacting with them for days, weeks, and even months.…”

“…Interactions with the corpse ranged from less than a day to less than a week in northern muriquis (Freire Filho et al, 2022) and Japanese macaques (Sugiyama et al, 2009), from 1-3 days to more than three months in chimpanzees (Soldati et al, 2022), and from one hour to more than 48 days in geladas (Fashing et al, 2011). When the care-taking lasts, the corpse bloats, stenches, decomposes, ends up covered with flies, mummifies until just fragments of it are left, and the remains no longer resemble an infant (Sugiyama et al, 2009;Watson & Matsuzawa, 2018).…”