Behavioral Ecology Advance Access originally published online on June 23, 2004
Behavioral Ecology 2004 15(6):898-906; doi:10.1093/beheco/arh092
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When are two heads better than one? Visual perception and information transfer affect vigilance coordination in foraging groups
a Department of Ecology, Evolution, and Behavior, University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108-6097, USA, and b Biology Department, Eastern Michigan University, Ypsilanti, MI 48197, USA
Address correspondence to E. Fernández-Juricic, who is now at the Department of Biological Sciences, California State University, Long Beach, Peterson Hall 1–109, 1250 Bellflower Blvd., Long Beach, CA 90840, USA. E-mail: efernand{at}csulb.edu.
Animals frequently raise their heads to check for danger. In a group, individuals generally raise their heads independently. Earlier models suggest that all group members could gain by coordinating their vigilance, i.e., each member raising its head when others are not. We re-examine these suggestions, considering groups of different sizes, in light of empirical findings that: (1) animals can sometimes detect a predator without raising their heads, and (2) when one member of a group detects a predator, the information does not always spread to other members of the group. Including these effects in models generally decreases the value of coordinated vigilance. Coordinated vigilance is highly favored only when animals have a low probability of detecting predators without lifting their heads but a high probability of being warned when another member of the group detects a predator. For other combinations, coordinated vigilance has little value and may have a negative value. Group size has contrasting effects depending on how social information is obtained. Coordination is favored in smaller groups when one or more detecting individuals provide a constant amount of information to individuals unaware of the predator. On the other hand, coordination is favored in larger groups if each detecting individual provides unaware individuals with an independent source of information (i.e., if the amount of information increases as the number of detecting individuals increases). These results depend on the balance of an escape due to social information and dilution of risk in groups with imperfect information spread. This framework could be tested by examining species with different visual fields and in different environments.
Key words: anti-predator behavior, collective detection, group size, risk dilution, scanning, vision.
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  O. Pays, A.-L. Dubot, P. J. Jarman, P. Loisel, and A. W. Goldizen Vigilance and its complex synchrony in the red-necked pademelon, Thylogale thetis Behav. Ecol., August 26, 2008; (2008) arn110v1. [Abstract] [Full Text] [PDF]
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