Moving in groups: how density and unpredictable motion affect predation risk

Nicholas E. Scott-Samuel*, Gavin Holmes, Roland Baddeley, Innes C. Cuthill

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

21 Citations (Scopus)


One of the most widely applicable benefits of aggregation is a per capita reduction in predation risk. Many factors can contribute to this but, for moving groups, an increased difficulty in tracking and targeting one individual amongst many has received particular attention. This “confusion effect” has been proposed to result from a bottleneck in information processing, a hypothesis supported by both modelling and experiment. If the competition for limited attention is localised to the particular part of the visual field where the target is located, prey density is likely to be the key factor rather than group numbers per se. Furthermore, unpredictability of prey movement may enhance confusion, but both factors have received insufficient attention from empiricists: undoubtedly because of the difficulty of experimental manipulation in natural systems. We used a computer-based target tracking task with human subjects to manipulate effects of number and density independently, in factorial combination with motion path predictability. Density, rather than number, drove the confusion effect in our experiment and acted synergistically with the unpredictability of the direction of motion. The experimental paradigm we present offers the potential for isolating other factors affecting predation success on group-living prey, and forging links with the psychological literature on object tracking and visual search.

Original languageEnglish
Pages (from-to)867-872
Number of pages6
JournalBehavioral Ecology and Sociobiology
Issue number6
Early online date24 Feb 2015
Publication statusPublished - 1 Jun 2015

Structured keywords

  • Cognitive Science
  • Visual Perception


  • Aggregation
  • Confusion effect
  • Group living
  • Object tracking
  • Predation risk
  • Visual search


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