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Research Article

Chimpanzees Share Forbidden Fruit

  • Kimberley J. Hockings mail,

    To whom correspondence should be addressed. E-mail: k.j.hockings@stir.ac.uk

    Affiliation: Department of Psychology, University of Stirling, Stirling, Scotland

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  • Tatyana Humle,

    Affiliation: Department of Psychology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America

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  • James R. Anderson,

    Affiliation: Department of Psychology, University of Stirling, Stirling, Scotland

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  • Dora Biro,

    Affiliation: Department of Zoology, University of Oxford, Oxford, United Kingdom

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  • Claudia Sousa,

    Affiliation: Department of Anthropology, New University of Lisbon, Lisbon, Portugal

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  • Gaku Ohashi,

    Affiliation: Primate Research Institute, Kyoto University, Kyoto, Japan

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  • Tetsuro Matsuzawa

    Affiliation: Primate Research Institute, Kyoto University, Kyoto, Japan

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  • Published: September 12, 2007
  • DOI: 10.1371/journal.pone.0000886

Reader Comments (7)

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Additional info and answers to Qs

Posted by hockingskim on 24 Jan 2008 at 15:27 GMT

Please find some additional information (FAQs) on chimpanzees crop sharing below:

How many and which other individuals were present at the consumption of any gathered crop?

This varied, but groups were often male-only and mixed composition (includes males, females and juveniles/infants). Please see p.116 of Hockings thesis (available on the internet) for exact info on group compositions and sizes during raids of individual crops.

Seeing that crops were shared only 1.5 times per month but gathered 22 times per month, what happened at those other times? Did possessors share with anyone approaching them, did they only share with particular individuals but deny others, etc? How high were success rates of food solicitation?

Crops were shared on 'average' 1.5 times per month (range of 0-7 bouts), but of course crop-raiding varied seasonally. This figure includes all cultivars, some of which were not shared at all during the observation period. This is why certain calculations focus on papaya sharing, the predominant cultivar shared. However, quite often, individuals would beg (all age- and sex-classes engaged in begging behaviours) but begging would not always be rewarded with food. I saw many occasions where adult males begged from each other but food was never shared. Additionally, unlike reports from other wild chimpanzee communities (e.g. Kibale, see Gilby), the Bossou chimpanzees did not form begging clusters, even though multiple individuals were present. However in the future, we do hope to collect additional quantitative data on begging intensities etc.

Was successful crop-raiding ever advertised in the way a successful hunt is to attract other group-members? That would strengthen the costly signalling hypothesis, because successful crop-raiders would have a bigger audience to signal their qualities to.

This is a nice point, and I agree that additional data would strengthen the costly signalling hypothesis. Although further research needs to be conducted, it became apparent that we could often predict when the chimpanzees would crop-raid according to their location in the forest and the direction they were heading, and group members (mostly females) who did not crop-raid, would wait in the forest next to where others (mostly males) were raiding, so would already know individuals were raiding - in this situation, for example, there is no need to advertise a 'successful raid', others already know. However I will think about this point some more and go back and look at my data set e.g. group sizes during sharing vs. non-sharing raids.

Did males always raid together, and if not, was overall and/or individual crop-raiding success influenced by number of male participants? If success correlated positively with number of participants one would expect more sharing among males as is the case with colobus hunting.

Not so much 'success' but males were more likely to crop-raid with other males than alone (see p. 123 of thesis). I agree that if males are indeed cooperating when crop-raiding (like you mentioned with colobus hunting at Tai) then we would expect sharing between males. This was never observed with fruits, even though raiding males sometimes did not secure a fruit (mostly due to lack of ripe fruits available) and males begged from other males. Due to the very small community size at Bossou and therefore lack of reproductively active females, there may be different forces shaping the males sharing behaviours. They may not need to share foods to strengthen bonds as there are only 3 adult males in the group, and competition for females is high?

How big were the proportions of transferred food?

We did not observe 'active' sharing, but instead 'tolerated theft' from out of the possessor's hands. In the case of papaya, the receiver would break off a piece whilst the possessor maintained possession. For the PLoS paper, we did not record exact food sizes, but a preliminary study does have some info on this (Ohashi 2007, Pan African News).

Was food transfer influenced by association patterns, i.e. did those who normally hung around males most get most food?

In terms of overall association patterns between all dyads, association patterns did not appear to influence sharing patterns e.g. Males spent most time together but never shared with each other. Also, the elderly females were often associated with other group members but did not frequently receive food during sharing events, even though present. It did appear that the adult males shared mostly with the 'preferred' female, who they also groomed more, as well as received more grooming from.