Elsevier

Animal Behaviour

Volume 54, Issue 4, October 1997, Pages 967-977
Animal Behaviour

Regular Article
Patch departure decisions by spice finches foraging singly or in groups

https://doi.org/10.1006/anbe.1997.0489Get rights and content

Abstract

The marginal value theorem predicts that when resources are clumped in space, a forager can maximize its rate of intake by deciding to leave a patch when its current feeding rate falls below the average for the habitat. A group version of the model predicts that when rate-maximizing group members share a patch, they should leave sooner, and each with less gain, than single animals exploiting the same patch. We tested these predictions in the laboratory by measuring patch departure decisions of spice finches,Lonchura punctulataexploiting food patches alone or in groups of three under two habitats that require different travel times. As predicted, group members left the patch sooner and with fewer seeds than single foragers. Unlike the model's assumptions, however, birds did not share the patch equally, and their exploitation curves could not be simply derived from those of single foragers. Grouping decreased the effect of travel time on patch exploitation. Moreover, within each group the bird expected to leave first delayed its departure although it collected fewer seeds than the others. This delayed departure could aim to maintain group membership. We noted an increased variability in seed number collected by group members compared with single foragers, which could be a cost of group foraging.

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    Krebs, J. R.Davies, N. B.

    f1

    Correspondence: L.-A. Giraldeau, Department of Biology, Concordia University, 1455 ouest, boul. de Maisonneuve, Montréal, Québec H3G 1M8, Canada (email: [email protected]).

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