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Eavesdropping foragers use level of collective commotion as public information to target high quality patches


M. E. Laidre, Dept of Integrative Biology, Univ. of California, 1005 Valley Life Sciences Bldg no. 3140, Berkeley, CA 94720-3140, USA. E-mail:


Public information offers a valuable means for social foragers to determine the relative quality of foraging patches. Despite much evidence that foragers use public information based on others’ feeding behavior, no experiments have examined whether foragers might use public information based on others’ competitive behavior, particularly the collective commotion that can be generated by aggregations. Such commotion could potentially provide a rich source of public information: as foragers compete in a patch with an especially high value resource, their heightened competition intensity could enable eavesdropping foragers to target this superior patch, based simply on its higher level of collective commotion. To test the hypothesis that the level of collective commotion is used as public information by eavesdropping foragers I conducted field experiments on terrestrial hermit crabs Coenobita compressus. These animals engage in collective competitive interactions in foraging patches for food and shells, generating variable levels of commotion across different quality patches. By experimentally manipulating the level of collective commotion in sham aggregations in the wild I show that a higher level of commotion is exploited by eavesdropping foragers to differentially target more valuable patches. Broadly, these results highlight an underappreciated significance of competitive by-products and higher- order collective pheno mena as forms of public information for foragers.