Deceased-infant carrying in nonhuman anthropoids: Insights from systematic analysis and case studies of bonnet macaques (Macaca radiata) and lion-tailed macaques (Macaca silenus).

Abstract

Existing models of attachment do not explain how death of offspring affects maternal behavior. Previous descriptions of maternal responsiveness to dead offspring in nonhuman anthropoids have not expounded the wide variation of deceased-infant carrying (DIC) behavior. Through the current study, we attempt to (a) identify determinants of DIC through a systematic survey across anthropoids, (b) quantitatively assess behavioral changes of mother during DIC, and (c) infer death perception of conspecifics. Firstly, we performed phylogenetic regression using duration of DIC as the dependent variable. Secondly, we undertook case studies of DIC in the bonnet monkey and the lion-tailed monkey through behavioral sampling. Results of phylogenetic Generalized Linear Mixed Model (Nspecies = 18; Ncases = 48) revealed a strong homology (H2 = 0.86). We also obtained a high intraspecific variation in DIC and found DIC to be affected by mother’s age, context of death, habitat condition, and degree of arboreality. We found bonnet mothers to carry their deceased offspring for 3.56 ± 4.03 SD days (N = 7) with diminished feeding, enhanced passivity, and social isolation during DIC and progressive decline in protection/attentiveness of corpse and attachment. Following Anderson (2016)’s framework of death perception, we interpreted repeated sensory investigation of corpses by mothers as comprehending causality of death, inanimate handling of corpse and its defense as comprehension of non-functionality, and a progressive disinterest of mothers in them as perceiving irreversibility of death. Lastly, we integrated DIC with mother-infant attachment theories and proposed a conceptual model characterizing DIC with causal determinants.

Death among primates: a critical review of non‐human primate interactions towards their dead and dying

“…and S1.4 of Appendix S1), compared to two‐thirds that were not ( N = 39) (Appendix S3). This finding supports the results of Das et al () and suggests that contextual and sensory death cues aid the mother's understanding of the infant's condition, allowing her to terminate her parental investment. Surprisingly, in 14 cases, infants were abandoned alive after being injured by an infanticidal male.…”

“…Das et al () found that carrying duration in cases of infanticide was significantly lower in comparison to other causes of death. They attribute three subcomponents typical of human death awareness to mothers carrying dead infants: repeated sensory investigation as a result of having ‘Causation’, handling of the inanimate infant and its defence as understanding ‘Cessation’, and progressive disinterest as possessing ‘Irreversibility’.…”

“…While she did not discuss any psychological mechanisms, it is highly likely on a proximate level that such decisions, through associative learning or higher cognitive mechanisms, are supported by contextual and physical cues of both injury and death. Other situations offering comparable sets of cues including predation (Matsuda, Tuuga & Higashi, ), mishandling and electrocution (Das et al , ) also lead to post‐mortem infant desertion.…”

Baboon thanatology: responses of filial and non-filial group members to infants' corpses

“…Observations of other behaviours by non-mothers lend further support to the social-bonds hypothesis. In three cases (7,10,11), an adult male-the friend of the mother and possible father of the dead infant in all cases-provided forms of post-mortem 'protection' involving 'guarding' behaviour by sitting near the corpse when the mother temporarily moved away, or by threatening perceived approaches to the corpse. Such guarding behaviour of an infant's corpse by an adult male has previously been reported in wild chacma baboons [27].…”

“…This hypothesis was not supported by a recent cross-species analysis of anthropoid primates (great apes, Old World and New World monkeys) that controlled for phylogenetic relatedness. The mother's age, the cause of the infant's death and the degree of the species' arboreality determined the length of time a corpse was carried [11].Intrinsic factors hypothesized to influence corpse carrying include cognitive, experiential and motivational/emotional processes. In the first case, the unawareness hypothesis suggests that the carrier is unaware or unsure that the infant is dead, and so they persist in performing infant-care behaviours, until awareness occurs.…”