Behavioral Ecology and Sociobiology

, Volume 63, Issue 9, pp 1331–1344 | Cite as

“Friendships” between new mothers and adult males: adaptive benefits and determinants in wild baboons (Papio cynocephalus)

  • Nga NguyenEmail author
  • Russell C. Van Horn
  • Susan C. Alberts
  • Jeanne Altmann
Original Paper


Close associations between adult males and lactating females and their dependent infants are not commonly described in non-monogamous mammals. However, such associations [sometimes called “friendships” (Smuts 1985)] are regularly observed in several primate species in which females mate with multiple males during the fertile period. The absence of mating exclusivity among “friends” suggests that males should invest little in infant care, raising questions about the adaptive significance of friendship bonds. Using data from genetic paternity analyses, patterns of behavior, and long-term demographic and reproductive records, we evaluated the extent to which friendships in four multi-male, multi-female yellow baboon (Papio cynocephalus) groups in Amboseli, Kenya represent joint parental care of offspring or male mating effort. We found evidence that mothers and infants benefited directly from friendships; friendships provided mother–infant dyads protection from harassment from other adult and immature females. In addition, nearly half of all male friends were the genetic fathers of offspring and had been observed mating with mothers during the days of most likely conception for those offspring. In contrast, nearly all friends who were not fathers were also not observed to consort with the mother during the days of most likely conception, suggesting that friendships between mothers and non-fathers did not result from paternity confusion. Finally, we found no evidence that prior friendship increased a male’s chances of mating with a female in future reproductive cycles. Our results suggest that, for many male–female pairs at Amboseli, friendships represented a form of biparental care of offspring. Males in the remaining friendship dyads may be trading protection of infants in exchange for some resources or services not yet identified. Our study is the first to find evidence that female primates gain social benefits from their early associations with adult males.


Male–female associations Parental care Mating effort Infant harassment 



We gratefully acknowledge the support of a National Science Foundation (NSF) Dissertation Improvement Grant to NN and JA as well as support to NN from the LSB Leakey Foundation and Princeton University. During this study, the Amboseli Baboon Project was supported by NSF grants IOB-0322613, IOB-0322781, BCS-0323553, and BCS-0323596 to JA and SCA. We thank the Republic of Kenya and the Kenya Wildlife Service for permission to work in Amboseli, the Institute of Primate Research for local sponsorship, and the Wardens and staff of Amboseli National Park and the pastoralist communities of Amboseli and Longido for continuous cooperation. R. Zimmerman designed the software program used to collect the behavioral data; Amboseli field workers R. S. Mututua, S. N. Sayialel, and J. K. Warutere provided field assistance and C. Markham and L. Gerber provided assistance with the Amboseli database. The manuscript benefited greatly from discussions with or comments by P. Fashing, M. Hau, D. Rubenstein, and two anonymous reviewers. All procedures were noninvasive and comply with relevant regulations in Kenya (Kenya Research Permit MOEST 13/001/C351 Vol. II) and the USA (IACUC 1456, renewed 12 November 2002).

Supplementary material

265_2009_786_MOESM1_ESM.doc (82 kb)
ESM Table S1 Identifying male friends from grooming and proximity data. Comparison of the identities of females’ most frequent male grooming and proximity partner(s) over the perinatal period for the 29 focal mothers. In cases where females spent equal amounts of time in proximity to each of two males, the names of both males are given. Females were seen in proximity to, but never grooming with, any adult males in four cases. Data are sorted by whether mothers’ grooming partner was the same individual as her proximity partner (Y) or not (N). (DOC 81 kb)
265_2009_786_MOESM2_ESM.doc (157 kb)
ESM Table S2 The characteristics of friendship bonds. The 29 mother–infant dyads included mothers and infants of all backgrounds. Male friends consisted of 16 of the 34 adult males resident in the four multi-male groups during the study period. (DOC 255 kb)
265_2009_786_MOESM3_ESM.doc (14 kb)
ESM Table S3 Comparison of prior mating success with mothers between friends who were fathers (Y) and friends who were not fathers (N). Females who consorted with males for less than 5 h during the fertile phase of the cycle in which the focal infant was conceived (indicated by gray highlighting) were not included in subsequent analyses. (DOC 13 kb)
265_2009_786_MOESM4_ESM.doc (81 kb)
ESM Table S4 Comparisons of fathers who were friends (Y) with fathers who were not friends (N) for the 23 mother–infant dyads for whom paternity could be assigned. (DOC 81 kb)
265_2009_786_MOESM5_ESM.doc (24 kb)
ESM Table S5 Comparisons of fathers who were friends with fathers who were not friends, using independent samples t tests. (DOC 45.0 kb)
265_2009_786_MOESM6_ESM.doc (16 kb)
ESM Table S6 Male mating success of former friends in future reproductive cycles. For male friends who were resident in the group on only a fraction of the days after their former friend resumed cycling, mating success was computed only from the period in which both friends were resident in the group together. Data are sorted by the proportion of months in which both friends were resident in the group after the focal female resumed cycling. (DOC 28.5 kb)


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Copyright information

© US Government 2009

Authors and Affiliations

  • Nga Nguyen
    • 1
    • 2
    • 3
    Email author
  • Russell C. Van Horn
    • 4
  • Susan C. Alberts
    • 5
    • 6
  • Jeanne Altmann
    • 6
    • 7
    • 8
  1. 1.Department of Conservation & ScienceCleveland Metroparks ZooClevelandUSA
  2. 2.Department of BiologyCase Western Reserve UniversityClevelandUSA
  3. 3.Department of AnthropologyCalifornia State University FullertonFullertonUSA
  4. 4.Conservation & Research for Endangered SpeciesZoological Society of San DiegoSan DiegoUSA
  5. 5.Department of BiologyDuke UniversityDurhamUSA
  6. 6.Institute for Primate ResearchNational Museums of KenyaNairobiKenya
  7. 7.Department of Ecology & Evolutionary BiologyPrinceton UniversityPrincetonUSA
  8. 8.Department of Animal Physiology and Veterinary MedicineUniversity of NairobiNairobiKenya

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