Title: Predation, scramble competition, and the vigilance group size effect in dark-eyed juncos (Junco hyemalis)
Author: Lima, Steven L.; Zollner, Patrick A.; Bednekoff, Peter A.;
Source: Behavioural Ecology and Sociobiology 46:110-116
Publication Series: Scientific Journal (JRNL)
Description: In socially feeding birds and mammals, as group size increases, individuals devote less time to scanning their environment and more time to feeding. This vigilance "group size effect" has long been attributed to the anti-predatory benefits of group living, but many investigators have suggested that this effect may be driven by scramble competition for limited food. We addressed this issue of causation by focusing on the way in which the scan durations of free-living dark-eyed juncos (Junco hyemalis) decrease with group size. We were particularly interested in vigilance scanning concomitant with the handling of food items, since a decrease in food handling times (i.e. scan durations) with increasing group size could theoretically be driven by scramble competition for limited food resources. However, we showed that food-handling scan durations decrease with group size in an environment with an effectively unlimited food supply. Furthermore, this food-handling effect was qualitatively similar to that observed in the duration of standard vigilance scans (scanning exclusive of food ingestion), and both responded to changes in the risk of predation (proximity of a refuge) as one might expect based upon anti-predator considerations. The group size effects in both food-handling and standard scan durations may reflect a lesser need for personal information about risk as group size increases. Scramble competition may influence vigilance in some circumstances, but demonstrating an effect of competition beyond that of predation may prove challenging.
Keywords: anti-predator behavior, food handling times, predation risk, scramble competition, sociality, vigilance, birds
- We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
- This publication may be available in hard copy. Check the Northern Research Station web site to request a printed copy of this publication.
- Our on-line publications are scanned and captured using Adobe Acrobat. During the capture process some typographical errors may occur. Please contact Sharon Hobrla, firstname.lastname@example.org if you notice any errors which make this publication unusable.
XML: View XML
Lima, Steven L.; Zollner, Patrick A.; Bednekoff, Peter A. 1999. Predation, scramble competition, and the vigilance group size effect in dark-eyed juncos (Junco hyemalis). Behavioural Ecology and Sociobiology 46:110-116
Get the latest version of the Adobe Acrobat reader or Acrobat Reader for Windows with Search and Accessibility