Vigilance benefits and competition costs in groups: do individual redshanks gain an overall foraging benefit?

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2007.11.005 Byline: Alex Sansom, Will Cresswell, Jeroen Minderman, Johan Lind Abstract: Animals gain antipredation benefits from being in larger groups through increased probability of predator detection, dilution of individual risk of being attacked and confusion of predators during attack. A further benefit is that individuals in larger groups can decrease the amount of time they spend being vigilant, while maintaining a high probability of predator detection. They may then gain extra time to forage, so increasing overall intake rate. Increasing group size, however, can also increase competition so that intake rates decrease. We investigated whether there was a foraging benefit in redshanks, Tringa totanus, that show the group size decrease in individual vigilance. Intake rates did not change with group size, despite an increase in time spent foraging. Interference competition increased with group size because individuals travelled more to find prey. Redshanks used the extra time available to forage to maintain intake rates under increased competition. Although the group size effect on vigilance did not accrue direct foraging benefits, larger groups formed, conferring other antipredation benefits. Intake rates were maintained because the interference competition was compensated by the benefits of reduced individual vigilance. Author Affiliation: (a) School of Biology, University of St. Andrews, U.K. (a ) School of Biology & Psychology, Newcastle University, U.K. (a ) Department of Zoology, Stockholm University, Sweden Article History: Received 8 June 2007; Revised 6 August 2007; Accepted 13 November 2007 Article Note: (miscellaneous) MS. number: 9411R