Rich pickings near large communal roosts favor 'gang' foraging by juvenile common ravens, Corvus corax
Public Library of Science (PLoS)
Copyright: 2009 Dall et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Ravens (Corvus corax) feed primarily on rich but ephemeral carcasses of large animals, which are usually defended by territorial pairs of adults. Non-breeding juveniles forage socially and aggregate in communal winter roosts, and these appear to function as 'information centers' regarding the location of the rare food bonanzas: individuals search independently of one another and pool their effort by recruiting each other at roosts. However, at a large raven roost in Newborough on Anglesey, North Wales, some juveniles have been observed recently to forage in 'gangs' and to roost separately from other birds. Here we adapt a general model of juvenile common raven foraging behavior where, in addition to the typical co-operative foraging strategy, such gang foraging behavior could be evolutionarily stable near winter raven roosts. We refocus the model on the conditions under which this newly documented, yet theoretically anticipated, gang-based foraging has been observed. In the process, we show formally how the trade off between search efficiency and social opportunity can account for the existence of the alternative social foraging tactics that have been observed in this species. This work serves to highlight a number of fruitful avenues for future research, both from a theoretical and empirical perspective.
This work was undertaken as an unfunded side project while SRXD was supported by grants to I. L. Boyd and T. H. Clutton-Brock (AFI1/03) and R. A. Johnstone (NER/A/S/2002/00898) by the Natural Environment Research Council (U.K.). These funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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Vol. 4: 4530
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