Male Tibetan macaques'(Macaca thibetana) choice of infant bridging partners
Briana Bauer1, Lori K Sheeran2, Megan D Matheson3
1Primate Behavior and Ecology Program, Central Washington University, WA 98926, USA. bbauer3@alumni.nd.edu.
Insights
Adult male macaques use infants for bridging, a behavior potentially linked to social dynamics. This study suggests male macaques prefer male infants for bridging, supporting the agonistic buffering hypothesis.
Area of Science:
- Primate behavior
- Social cognition
- Ethology
Background:
- Adult male macaques engage in infant handling, termed "bridging."
- The function of bridging is debated, with hypotheses including paternal care, mating effort, and agonistic buffering.
- Previous research indicates a bias towards using male infants for bridging.
Purpose of the Study:
- To investigate whether adult males' affiliative relationships with females predict infant use in bridging behavior.
- To examine biases in sex, age, and individual selection of infants for bridging by male macaques.
- To test the agonistic buffering hypothesis in Tibetan macaques (Macaca thibetana).
Main Methods:
- Observational study of a habituated, provisioned group of Tibetan macaques.
- Data collection using all occurrences, focal animal, and scan sampling methods.
- Analysis of male-infant interactions and male-female affiliative relationships.
Main Results:
- Male infants were significantly preferred over female infants for bridging.
- Bridging infant selection showed individual biases, with one male infant used more frequently than others.
- Adult males' affiliative relationships with females did not consistently predict their choice of bridging infant, except in one case linked to the infant's mother.
- Lower-ranked males preferentially used the alpha male's preferred infant.
Conclusions:
- Results support the agonistic buffering hypothesis, suggesting bridging may be used by lower-ranked males to manage interactions with dominant individuals.
- Bridging behavior in Tibetan macaques is influenced by social rank and the need to regulate potentially antagonistic encounters.
- The function of bridging is complex and likely involves multiple social factors beyond direct paternal care or mating effort.
Abstract:
Adult male Tibetan (Macaca thibetana), Barbary (M. sylvanus), and stump-tailed macaques (M. arctoides) engage in bridging, a ritualized infant-handling behavior. Previous researchers found a bias toward the use of male infants for this behavior, but its function is debated. Explanations include three hypotheses: paternal care, mating effort, and agonistic buffering. We studied a group of habituated, provisioned Tibetan macaques to test whether adult males' affiliative relationships with females predicted their use of an infant for bridging. We also examined biases for sex, age, and individual in males' choice of bridging infant. We collected data via all occurrences, focal animal, and scan methods, from August to September 2011 at the Valley of the Wild Monkeys, China. We found that male infants were significantly preferred over females for bridging, but of three male infants in the group, only one was used by all males, while one male infant was used less often than expected. Adult males had females they were significantly more likely to be proximate to and/or to groom, but these corresponded to the mother of the bridging infant for only one male. Our results are most consistent with the agonistic buffering hypothesis: lower-ranked males used the alpha male's preferred bridging infant in an attempt to regulate their interactions with the alpha.
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