Interchange between grooming and infant handling in female Tibetan macaques (Macaca thibetana)

All together now: Assessing variation in maternal and nonmaternal handling of wild Colobus vellerosus infants

Primatologists have a long-standing interest in the study of maternal care and nonmaternal handling (NH) of infants stemming from recognition that early social relationships can have enduring consequences. Though maternal care and NH often include expression of similar behaviors, they are regularly studied in isolation from each other with nonoverlapping terminology, thereby overlooking possible interplay between them and obfuscating potential developmental ramifications that ensue from trade-offs made between maternal (MH) and NH during infancy. To that end, identifying how MH and NH patterns interact and contribute to the total handling (TH) infants receive is a critical first step. We present durational handling data collected from 25 wild Colobus vellerosus infants from 2016 to 2017 and assess the relationships between TH, MH, and NH. Patterns of social affiliation are shaped in part by surrounding context, and therefore, we also assess whether NH and TH differ in their responsivity to various infant and social group characteristics. Ninety-four percent of observed handling was MH, while just 5.5% was NH. Young infants who received more MH (excluding nursing) also received more NH; there was no relationship between the two in older infants. Infants in larger groups participated in more handling of all types. Additionally, NH time was associated with infant sex and group stability. Non-nursing TH time was associated with group stability and infant cohort size. Though NH variation likely confers social-networking advantage, in this population NH is not a major contributor to TH and would not effectively replace reduced MH. The positive association between MH and NH during early infancy suggests that colobus mothers may play a mediating role in shaping infant socialization. This is a first step in elucidating how different forms of handling relate to one another in wild primates and in identifying the impact of handling on infant socialization.

Behavioral adaptation in an adoptive free-ranging female Tibetan macaque

Adoption is an important form of allomaternal care in nonhuman primates, with implications for reproductive output and infant survival. Here, we report a kidnapping that became an adoption of a 3-week-old infant by a mother with her own infant in Tibetan macaques (Macaca thibetana). The adoptive mother nursed her "new" infant (allonursing), the first observation of this behavior in the species. The case provided a natural experiment for comparing how a female copes with a heavier burden of care for both her biological infant and another female's infant, compared to mothers caring for only one infant. Our results showed that the adoptive female spent more time foraging and resting, and less time in group social activity compared to females with a single infant. The adoptive female showed more instances of social bridging. Although the duration of post-bridging grooming received from group members decreased, the frequency of such grooming increased. We discuss this adoption with reference to possible factors involved in the evolution of adoption and allonursing behavior in Tibetan macaques.

Opportunistic availability of an infant and social relationship to a mother influence grooming before infant handling in Japanese macaques

Biological market theory (BMT) predicts that the balance between supply and demand determines the economic value of a "commodity," which consequently determines the amount of "services" that an individual needs to provide to obtain the commodity. In infant handling among primates, the existing literature suggests that handlers need to groom a mother to obtain access to its infant, particularly when the value of the infant is high (e.g., when the number of infants is low). However, grooming by handlers may not be a prerequisite for the occurrence of infant handling, because handlers can handle an infant that is separated from its mother. Based on 3 years of behavioral observations of wild Japanese macaques (Macaca fuscata), we examined the process by which infant handling occurs and the role of grooming in infant handling. We found that infant handling occurred more frequently when the mother and infant were separated than when they were in contact. Grooming rarely occurred before infant handling. The subsequent occurrence of infant handling was not predicted by either the occurrence or duration of grooming toward mothers by non-mother individuals. Grooming by handlers was also more likely to occur when an infant was in contact with its mother and when an infant's mother was dominant to the handlers. Contrary to BMT, the number of infants in a group did not affect grooming by handlers. These results indicate that the handlers' decision to groom depended on the opportunistic availability of an infant and the social relationship between the infant's mother and themselves. We conclude that grooming was not always necessary for infant handling.

Variation in communicative complexity in relation to social structure and organization in non-human primates

Communicative complexity relates to social complexity, as individuals in more complex social systems either use more signals or more complex signals than individuals living in less complex ones. Taking the individual group member's perspective, here we examine communicative complexity in relation to social complexity, which arises from two components of social systems: social structure and social organization. We review the concepts of social relationships and social complexity and evaluate their implications for communicative and cognitive complexity using examples from primate species. We focus on spider monkeys (Ateles geoffroyi), as their social organization is characterized by flexibility in grouping dynamics and they use a variety of communicative signals. We conclude that no simple relationship exists among social complexity, communicative complexity and cognitive complexity, with social complexity not necessarily implying cognitive complexity, and communicative and cognitive complexity being independently linked to social complexity. To better understand the commonly implied link between social complexity and cognitive complexity it is crucial to recognize the complementary role of communicative complexity. A more elaborated communicative toolkit provides the needed flexibility to deal with dynamic and multifaceted social relationships and high variation in fission-fusion dynamics. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.