Contagious fear: Escape behavior increases with flock size in European gregarious birds

Federico Morelli, Yanina Benedetti, Mario Diaz, Tomas Grim, Juan Diego Ibáñez-Álamo, Jukka Jokimaki, Marja-Liisa Kaisanlahti-Jokimaki, Kunter Tätte, Gábor Markó, Yiting Jiang, Piotr Tryjanowski, Anders Pape Møller

Research output: Contribution to journalArticleScientificpeer-review

41 Citations (Scopus)


Flight initiation distance (FID), the distance at which individuals take flight when approached by a potential (human) predator, is a tool for understanding predator–prey interactions. Among the factors affecting FID, tests of effects of group size (i.e., number of potential prey) on FID have yielded contrasting results. Group size or flock size could either affect FID negatively (i.e., the dilution effect caused by the presence of many individuals) or positively (i.e., increased vigilance due to more eyes scanning for predators). These effects may be associated with gregarious species, because such species should be better adapted to exploiting information from other individuals in the group than nongregarious species. Sociality may explain why earlier findings on group size versus FID have yielded different conclusions. Here, we analyzed how flock size affected bird FID in eight European countries. A phylogenetic generalized least square regression model was used to investigate changes in escape behavior of bird species in relation to number of individuals in the flock, starting distance, diet, latitude, and type of habitat. Flock size of different bird species influenced how species responded to perceived threats. We found that gregarious birds reacted to a potential predator earlier (longer FID) when aggregated in large flocks. These results support a higher vigilance arising from many eyes scanning in birds, suggesting that sociality may be a key factor in the evolution of antipredator behavior both in urban and rural areas. Finally, future studies comparing FID must pay explicit attention to the number of individuals in flocks of gregarious species.

Original languageEnglish
Pages (from-to)6096-6104
JournalEcology and Evolution
Issue number10
Publication statusPublished - 1 May 2019
MoEC publication typeA1 Journal article-refereed

Field of science

  • Ecology, evolutionary biology


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