Why chimpanzee (Pan troglodytes schweinfurthii) mothers are less gregarious than nonmothers and males: the infant safety hypothesis |
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Authors: | Emily Otali Jason S Gilchrist |
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Institution: | (1) Institute of Environment and Natural Resources, Makerere University, P.O. Box 7298, Kampala, Uganda;(2) Department of Anthropology, Harvard University, Peabody Museum, 11 Divinity Avenue, Cambridge, MA 02138, USA;(3) Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, England;(4) School of Life Sciences, Napier University, 10 Colinton Road, Edinburgh, EH10 5DT, Scotland |
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Abstract: | 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. |
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Keywords: | Chimpanzee Gregariousness Mother− offspring Pan troglodytes Proximity |
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