Back to the basics of anti-predatory vigilance: the group-size effect

摘要: Abstract A negative relationship between group size and levels of individual vigilance is widespread in socially feeding vertebrates. The main explanation this ‘group-size effect’, the many-eyes hypothesis, based on simple premise that as increases, there are progressively more eyes scanning environment for predators. Thus an forager can devote less time to (and feeding) increases without any lessening group's ability detect attack. Basic hypothesis assumption collective detection: all members alerted attack long it detected by at least one individual. In addition, important presumption associated with individuals monitor behaviour their groupmates determining own level vigilance. Neither idea detection nor behavioural monitoring received strong support experimental study mixed flocks dark-eyed juncos, Junco hyemalis, American tree sparrows, Spizella arborea. lack was particularly evident; however, some degree apparent. It possible anti-predatory rules-of-thumb may explain group-size effect while keeping intact basics hypothesis.