Selfish-herd behaviour of sheep under threat

• Published in: Current biology Vol. 22; no. 14; pp. R561 - R562
• Main Authors: King, Andrew J., Wilson, Alan M., Wilshin, Simon D., Lowe, John, Haddadi, Hamed, Hailes, Stephen, Morton, A. Jennifer
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 24.07.2012
• Subjects: Animals; dogs; Dogs - physiology; evolution; eyes; flocks; Food Chain; Geographic Information Systems; global positioning systems; group behavior; herding; herds; Models, Biological; Movement; predation; predators; Predatory Behavior; risk; schools of fish; sheep; Sheep, Domestic - physiology; Social Behavior; South Australia; swarms; South Australia
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2012.05.008

Flocking is a striking example of collective behaviour that is found in insect swarms, fish schools and mammal herds [1]. A major factor in the evolution of flocking behaviour is thought to be predation, whereby larger and/or more cohesive groups are better at detecting predators (as, for example, in the ‘many eyes theory’), and diluting the effects of predators (as in the ‘selfish-herd theory’) than are individuals in smaller and/or dispersed groups [2]. The former theory assumes that information (passively or actively transferred) can be disseminated more effectively in larger/cohesive groups, while the latter assumes that there are spatial benefits to individuals in a large group, since individuals can alter their spatial position relative to their group-mates and any potential predator, thus reducing their predation risk [3]. We used global positioning system (GPS) data to characterise the response of a group of ‘prey’ animals (a flock of sheep) to an approaching ‘predator’ (a herding dog). Analyses of relative sheep movement trajectories showed that sheep exhibit a strong attraction towards the centre of the flock under threat, a pattern that we could re-create using a simple model. These results support the long-standing assertion that individuals can respond to potential danger by moving towards the centre of a fleeing group [2].