In comparative thanatology, most reports for nonhuman mammals concern mothers' behavioural responses to their dead offspring: most prominently, dead-infant carrying (sometimes of extended duration); but also inspection, proximity, maternal care such as grooming, protective behaviours and filial cannibalism. Documented across many primate species, these behaviours remain poorly understood in all. The literature is dominated by relatively brief qualitative descriptions of isolated anecdotal cases in apes and monkeys. We argue for quantitative coding in case reports, alongside analyses of longitudinal records of such events to allow objective evaluation of competing theories, and systematic comparisons within and across species and populations. Obtaining necessary datasets depends on raised awareness in researchers of the importance of recording occurrences and knowledge of pertinent data to collect. We review proposed explanatory hypotheses and outline data needed to test each empirically. To determine factors influencing infant-corpse carriage, we suggest analyses of deaths resulting in 'carry' versus 'no carry'. For individual cases, we highlight behavioural variables to code and the need for hormonal samples. We discuss mothers' stress and welfare in relation to infant death, continued transportation and premature removal of the corpse. Elucidating underlying proximate and ultimate causes is important for understanding phylogeny of maternal responses to infant death.This article is part of the theme issue 'Evolutionary thanatology: impacts of the dead on the living in humans and other animals'.

Researchers have demonstrated the neighbor effect for affiliative and agonistic neighbor vocalizations in captive chimpanzees. We extend the investigation of the neighbor effect to New World monkeys, Callithrix jacchus. We collected data on vocalizations and behaviors of 31 focal individuals and concurrent neighbor vocalization within three behavioral categories: intragroup and intergroup aggression and intragroup affiliation. We investigated whether there was an influence of neighbor vocalizations on focal behavior within the same behavioral category. For data analysis we used approximate randomization of paired-sample t-tests. We found that marmosets performed intergroup aggressive behavior (bristle, anogenital present for neighbor loud shrill only) for significantly longer, and emitted significantly more intergroup agonistic vocalizations (twitter, loud shrill), at a high frequency of intergroup agonistic neighbor vocalizations (twitter, loud shrill) than at low. The marmosets were also significantly more likely to engage in bristle behavior immediately after hearing a neighbor intergroup aggressive call (twitter, loud shrill) than directly beforehand. High neighbor intragroup agonistic calls (chatter) were associated with significantly longer spent in related behavior (composite of: attack, chase, steal food). Affiliative behaviors (share food, grooming invite) were engaged in by marmosets for significantly longer at higher frequencies of affiliative neighbor chirp calls than at low. Marmosets were also significantly more likely to perform food sharing and active affiliative contact immediately after rather than before hearing a neighbor chirp call. Our findings suggest that neighbor vocalizations influence marmoset behavior through social contagion and indicate that the neighbor effect for affiliation and aggression generalizes to the marmoset.

Recently, several researchers have highlighted the neglect of social behaviors relative to food-related behaviors in experimental research on social learning in primates, despite the significant number of apparent social traditions reported in the field. Here we aim to highlight the discrepancy between the relative number of nonfood-related behavioral traditions reported in the wild and foodrelated ones, and the almost exclusive investigation of food-related behaviors in an experimental context. First we discuss aspects of social and communicative customs that make them especially interesting. Then we consider reasons why experimental approaches are crucial to developing a full understanding of behavioral traditions observed in the wild. We report the results of a systematic literature survey in which we assessed the perceived discrepancy quantitatively. We also argue that the existing experimental literature, with its typical reliance on food as a motivator, may not be sufficient to elucidate the mechanisms underlying nonfood traditions, such as social conventions. Finally, we suggest new directions for the experimental investigation of social learning in primates, hoping to stimulate experimental research investigating social and communicative behavioral traditions.

Cultural variation can be conceptualised in two main ways: as culture-specific qualitative differences in behavioural form, and also as quantitative variation in performance of constellations of universal behaviours (cultural style). Despite observation of both types in wild non-human primates, diffusion of qualitative culture has been scrutinised extensively experimentally whilst within-species transmission of cultural style has remained entirely unexplored. Here we investigated whether a cultural style of high affiliation could be artificially generated in a nonhuman primate (Callithrix jacchus), by daily playback of conspecific affiliative calls simulating nearby amicable individuals. We found that vocalisation playback influenced monkeys to spend more time in affiliative behaviours outwith playback hours, relative to silent playback. The effect was specific to affiliation, with no impact on other categories of affect. This change did not persist into the final phase of observation after all playbacks were complete. Findings are consistent with a temporary shift in cultural style effected through vocalisation playback, supporting existence of this conception of culture in wild primates and indicating auditory social contagion as a potential diffusion mechanism. The method presented here will allow researchers to test hypotheses concerning cultural transmission of cultural style, and the underlying processes, across a range of contexts and species

Although commercially available complete diets exist for common marmosets, the animals' consumption of these diets (available in dry pellet form) is typically very low. Increasing consumption of the pellet diet could have positive consequences for the welfare of the marmosets as the pellets are designed specifically to meet their full nutritional requirements, and therefore an increase in intake should help to ensure that they take in an appropriate balance of nutrients. We carried out a series of studies targeted towards improving the palatability, and hence increasing the intake, of a complete dry pellet diet for marmosets. In Study 1 we attempted to determine which of a wide range of flavours appeared to be preferred by the marmosets. In Study 2 we tested the marmosets' preferences for a smaller number of highly preferred flavours (as determined in Study 1) when actually added to the dry pellet diet in a series of paired preference tests. Finally, in Study 3 we tested whether adding the most highly preferred flavours (as determined in Study 2) to the dry pellet diet would in fact increase consumption of these pellets in comparison with unflavoured pellets. Despite finding strong and consistent preferences for particular flavours amongst the marmosets, we found that adding these to the pellets did not significantly increase consumption. Reasons for this are discussed, along with other potential modifications which might prove more successful in increasing consumption of pellet diets for marmosets.