Behavioral Ecology and Sociobiology

, Volume 59, Issue 4, pp 561–570 | Cite as

Why chimpanzee (Pan troglodytes schweinfurthii) mothers are less gregarious than nonmothers and males: the infant safety hypothesis

  • Emily OtaliEmail author
  • Jason S. Gilchrist
Original Article


Socialization of young is an important component of maternal care in social mammals. It is therefore perplexing that female chimpanzees with dependent offspring spend more time alone than females without dependent offspring, and than males. We propose that chimpanzee mothers are less gregarious than nonmothers and males to reduce the risk of injury that aggressive males pose to their offspring. We predict that mothers will associate less with males, associate with fewer males, and reduce mother−infant proximity in the presence of males, and that these effects will reduce with increasing offspring age. We test whether the pattern of gregariousness and mother−offspring proximity support these predictions in the Kanyawara chimpanzee community in Uganda. The probability that a female was found in the presence of males was lower for mothers than nonmothers and increased with offspring age. The probability that a female was found with other females did not differ between mothers and nonmothers. Mother-to-offspring distance was higher when a mother was in an all-female group than in a mixed-sex group and increased with her offspring's age. Mother-to-offspring distance was greatest when there were relatively low numbers of males and relatively high numbers of females in a subgroup. We propose that mothers avoid grouping with males because of the vulnerability of their young, and that the presence of males in a subgroup increases a female's protectiveness of her young. We discuss the implications of our findings and the relevance of fission−fusion group formation to chimpanzee mothers.


Chimpanzee Gregariousness Mother−offspring Pan troglodytes Proximity 



E.O. received the following funding for this research: Compton Foundation Fellowship, Franklin Mosher Baldwin Fellowship (L.S.B. Leakey Foundation) financial and logistical support during analysis and write-up from the Harvard University Graduate School of Arts and Sciences, and Conservation International. We thank the Uganda Wildlife Authority and the Uganda National Council for Science and Technology for permission to conduct this study. Assistance with fieldwork was given by C. Muruuli, J. Basigara, P. Tuhairwe, F. Mugurusi, D. Sebugwawo, and the late D. Muhangi. We thank Richard Wrangham, Charles Nunn, and three anonymous referees for comments on the manuscript. We are grateful to Richard Wrangham, Gilbert Isabirye-Basuta, Tim Clutton-Brock, Colin Chapman, David Watts, John Mitani, Andrew Russell, Redouan Bshary, John Kasenene, Vernon Reynolds, Derek Pomeroy, Christine Dranzoa, Panta Kasoma, Kim Duffy, Sonya Kahlenberg, Katharine Pieta, Melissa Emery Thompson, Zarin Machanda, and Eva Laier for comments and advice at various stages of this study.


  1. Altmann J, Samuels A (1992) Costs of maternal care: infant carrying in baboons. Behav Ecol Sociobiol 29:391−398CrossRefGoogle Scholar
  2. Arcadi AC, Wrangham RW (1999) Infanticide in chimpanzees: review of cases and a new within-group observation from the Kanyawara study group in Kibale National Park. Primates 42:337-351CrossRefGoogle Scholar
  3. Barrett L, Dunbar RIM, Dunbar P (1995) Mother−infant contact as contingent behaviour in gelada baboons. Anim Behav 49:805−810Google Scholar
  4. Boesch C (1997) Evidence for dominant wild female chimpanzees investing more in sons. Anim Behav 54:811−815PubMedCrossRefGoogle Scholar
  5. Boesch C, Boesch-Achermann H (2000) The chimpanzees of the Tai forest: behavioural ecology and evolution. Oxford University Press, New YorkGoogle Scholar
  6. Brent L, Bramblett CA, Bard KA, Bloomsmith MA, Blangero J (1997) The influence of siblings on wild infant chimpanzee social interaction. Behaviour 134:1189−1210Google Scholar
  7. Cairns SJ, Schwager SJ (1987) A comparison of association indices. Anim Behav 35:1454−1469CrossRefGoogle Scholar
  8. Cameron EZ, Linklater WL, Stafford KJ, Minot EO (2003) Social grouping and maternal behaviour in feral horses (Equus caballus): the influence of males on maternal protectiveness. Behav Ecol Sociobiol 53:92−101Google Scholar
  9. Chapman CA, Wrangham RW (1993) Range use of the chimpanzees of Kibale: implications for the evolution of chimpanzee social organisation. Am J Primatol 31:263−273CrossRefGoogle Scholar
  10. Chapman CA, Wrangham RW, Chapman LJ (1995) Ecological constraints on group size: an analysis of spider monkey and chimpanzee subgroups. Behav Ecol Sociobiol 36:59−70CrossRefGoogle Scholar
  11. Clark AP, Wrangham RW (1994) Chimpanzee arrival pant-hoots: do they signify food or status? Int J Primatol 15:185−205CrossRefGoogle Scholar
  12. Clutton-Brock TH (1991) The evolution of parental care. Princeton University Press, PrincetonGoogle Scholar
  13. Clutton-Brock TH, Brotherton PNM, O'Riain MJ, Griffin AS, Gaynor D, Kansky R, Sharpe L, McIlrath GM (2001) Contributions to cooperative rearing in meerkats. Anim Behav 61:705−710CrossRefGoogle Scholar
  14. Dunbar RIM (1988) Primate social systems. Cornell University Press, New YorkGoogle Scholar
  15. Elston DA (1998) Estimation of denominator degrees of freedom of F-distributions for assessing Wald statistics for fixed-effect factors in unbalanced mixed models. Biometrics 54:1085−1096CrossRefGoogle Scholar
  16. Fairbanks LA (1996) Individual differences in maternal style: causes and consequences for mothers and offspring. Adv Study Behav 25:579−611CrossRefGoogle Scholar
  17. Genstat 5 Committee (2002) Genstat 5 reference manual. Clarendon, OxfordGoogle Scholar
  18. Goodall J (1997) Infant killing and cannibalism in free-living chimpanzees. Folia Primatol 28:259−282PubMedGoogle Scholar
  19. Goodall J (1986) The chimpanzees of Gombe: patterns of behaviour. The Belknap Press of Harvard University Press, CambridgeGoogle Scholar
  20. Hamai M, Nishida T, Takasaki H, Turner LA (1992) New records of within-group infanticide and cannibalism in wild chimpanzees. Primates 133:151−162CrossRefGoogle Scholar
  21. Isabirye-Basuta G (1988) Food competition among individuals in a free-ranging chimpanzee community in Kibale forest, Uganda. Behaviour 105:135−147Google Scholar
  22. Janson CH, Goldsmith ML (1995) Predicting group size in primates: foraging costs and predation risks. Behav Ecol 6:326−336CrossRefGoogle Scholar
  23. Lehmann J, Boesch C (2004) To fission or to fusion: effects of community size on wild chimpanzee (Pan troglodytes verus) social organisation. Behav Ecol Sociobiol 56:207−216CrossRefGoogle Scholar
  24. Maestripieri D (2002) Parent−offspring conflict in primates. Int J Primatol 23:923−951CrossRefGoogle Scholar
  25. Maestripieri D, Megna NL, Ross SK (2002) Mother−infant interactions in western lowland gorillas (Gorilla gorilla gorilla): spatial relationships, communications, and opportunities for social learning. J Comp Psychol 116:219−227PubMedCrossRefGoogle Scholar
  26. Matsumoto-Oda A (1999) Mahale chimpanzees: grouping patterns and cycling females. Am J Primatol 47:197−207PubMedCrossRefGoogle Scholar
  27. Mitani JC, Amsler SJ (2003) Social and spatial aspects of male subgrouping in a community of wild chimpanzees. Behaviour 140:869−884CrossRefGoogle Scholar
  28. Muller MN (2002) Agonistic relations among Kanyawara chimpanzees. In: Boesch C, Hohmann G, Marchant LF (eds) Behavioural diversity in chimpanzees and bonobos. Cambridge University Press, Cambridge, pp 112−124Google Scholar
  29. Newton-Fisher NE (1999) Association by male chimpanzees: a social tactic? Behaviour 136:705−730CrossRefGoogle Scholar
  30. Newton-Fisher NE, Reynolds V, Plumptre AJ (2000) Food supply and chimpanzee (Pan troglodytes schweinfurthii) party size in Budongo Forest Reserve, Uganda. Int J Primatol 21:613−628CrossRefGoogle Scholar
  31. Nishida T, Corp N, Hamai M, Hasegawa T, Hiraiwa-Hasegawa M, Hosaka K, Hunt KD, Itoh N, Kawanaka K, Matsumoto-Oda A, Mitani JC, Nakamura M, Norikoshi K, Sakamaki T, Turner L, Uehara S, Zamma K (2003) Demography, female life history, and reproductive profiles among the chimpanzees of Mahale. Am J Primatol 59:99−121PubMedCrossRefGoogle Scholar
  32. Pepper JW, Mitani JC, Watts DP (1999) General gregariousness and specific social preferences among wild chimpanzees. Int J Primatol 20:613−632CrossRefGoogle Scholar
  33. Pusey AE, Williams J, Goodall J (1997) The influence of dominance rank on the reproductive success of female chimpanzees. Science 277:828−831PubMedCrossRefGoogle Scholar
  34. Sakura O (1994) Factors affecting party size and composition of chimpanzees (Pan troglodytes verus) at Bossou, Guinea. Int J Primatol 15:167−183CrossRefGoogle Scholar
  35. Schall R (1991) Estimation of generalised linear models with random effects. Biometrika 78:719−727CrossRefGoogle Scholar
  36. Smuts BB (1985) Sex and friendship in baboons. Aldine, New YorkGoogle Scholar
  37. Sokal RR, Rohlf FJ (1995) Biometry: the principles and practice of statistics in biological research, 3rd edn. Freeman, New YorkGoogle Scholar
  38. Struhsaker TT (1997) The ecology of an African rain forest: logging in Kibale and the conflict between conservation and exploitation. University Press of Florida, GainesvilleGoogle Scholar
  39. Sugiyama Y (1973) The social structure of wild chimpanzees: a review of field studies. In: Mitchel RP, Crook JH (eds) Comparative ecology and behaviour of primates. Academic, London, pp 375−410Google Scholar
  40. Treves A, Drescher A, Snowdon CT (2003) Maternal watchfulness in black howler monkeys (Alouatta pigra). Ethology 109:135−146CrossRefGoogle Scholar
  41. Trivers RL (1974) Parent−offspring conflict. Am Zool 14:249−264Google Scholar
  42. Tutin CEG (1979) Mating patterns and reproductive strategies in a community of wild chimpanzees. Behav Ecol Sociobiol 6:29−38CrossRefGoogle Scholar
  43. Vigilant L, Hofreiter M, Siedel H, Boesch C (2001) Paternity and relatedness in wild chimpanzee communities. Proc Natl Acad Sci U S A 23:12890−12895CrossRefGoogle Scholar
  44. Watts DP (2000) Grooming between male chimpanzees at Ngogo, Kibale National Park. I. Partner number and diversity and grooming reciprocity. Int J Primatol 21:189−210CrossRefGoogle Scholar
  45. Watts DP, Mitani JC (2000) Infanticide and cannibalism by male chimpanzees at Ngogo, Kibale National Park, Uganda. Primates 41:357−365CrossRefGoogle Scholar
  46. Watts DP, Mitani JC (2001) Boundary patrols and intergroup encounters in wild chimpanzees. Behaviour 138:299−327CrossRefGoogle Scholar
  47. Williams JM, Hsien-Yang L, Pusey AE (2002) Costs and benefits of grouping for female chimpanzees at Gombe. In: Boesch C, Hohmann G, Marchant LF (eds) Behavioural diversity in chimpanzees and bonobos. Cambridge University Press, Cambridge, pp 192−203Google Scholar
  48. Wrangham RW (1980) An ecological model of female-bonded primates. Behaviour 75:262−300Google Scholar
  49. Wrangham RW (1999) Evolution of coalitionary killing. Yearb Phys Anthropol (Wash) 42:1−30CrossRefGoogle Scholar
  50. Wrangham RW (2000) Why are male chimpanzees more gregarious than mothers? A scramble competition hypothesis. In: Kappeler PM (ed) Male primates. Cambridge University Press, Cambridge, pp 248−258Google Scholar
  51. Wrangham RW, Chapman CA, Clark AP, Isabirye-Basuta G (1996) Social ecology of Kanyawara chimpanzees; implications for understanding the costs of great ape groups. In: McGrew W, Marchant LF, Nishida T (eds) Great ape societies. Cambridge University Press, Cambridge, pp 45−57Google Scholar
  52. Wrangham RW, Clark AP, Isabirye-Basuta G (1992) Female social relationships and social organisation of Kibale forest chimpanzees. In: Nishida T, McGrew W, Marler P, Pickford M, de Waal F (eds) Topics of primatology, vol 1. University of Tokyo Press, Tokyo, pp 81−98Google Scholar
  53. Wrangham RW, Conklin NL, Chapman CA, Hunt KD (1991) The significance of fibrous foods for Kibale Forest chimpanzees. Phil Trans R Soc Lond B Biol Sci 334:171−178CrossRefGoogle Scholar
  54. Wrangham RW, Gittleman JL, Chapman CA (1993) Constraints on group size in primates and carnivores: population density and day-range as assays of exploitation competition. Behav Ecol Sociobiol 32:199−209CrossRefGoogle Scholar
  55. Wrangham RW, Peterson D (1996) Demonic males: apes and the origins of human violence. Houghton Mifflin, BostonGoogle Scholar
  56. Wrangham RW, Smuts BB (1980) Sex differences in the behavioural ecology of chimpanzees in the Gombe National Park, Tanzania. J Reprod Fertil Suppl Suppl 28:13−31Google Scholar

Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  1. 1.Institute of Environment and Natural ResourcesMakerere UniversityKampalaUganda
  2. 2.Department of AnthropologyHarvard UniversityCambridgeUSA
  3. 3.Department of ZoologyUniversity of CambridgeCambridgeEngland
  4. 4.School of Life SciencesNapier UniversityEdinburghScotland

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