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Absence of “selfish herd” dynamics in bird flocks under threat

2021; Elsevier BV; Volume: 31; Issue: 14 Linguagem: Inglês

10.1016/j.cub.2021.05.009

1879-0445

Daniel W. E. Sankey, Rolf F. Storms, Robert Musters, Timothy Russell, Charlotte K. Hemelrijk, Steven J. Portugal,

Animal Vocal Communication and Behavior

The "selfish herd" hypothesis1Hamilton W.D. Geometry for the selfish herd.J. Theor. Biol. 1971; 31: 295-311Crossref PubMed Scopus (2435) Google Scholar provides a potential mechanism to explain a ubiquitous phenomenon in nature: that of non-kin aggregations. Individuals in selfish herds are thought to benefit by reducing their own risk at the expense of conspecifics by attracting toward their neighbors' positions1Hamilton W.D. Geometry for the selfish herd.J. Theor. Biol. 1971; 31: 295-311Crossref PubMed Scopus (2435) Google Scholar,2Krause J. Tegeder R.W. The mechanism of aggregation behaviour in fish shoals: individuals minimize approach time to neighbours.Anim. Behav. 1994; 48: 353-359Crossref Scopus (53) Google Scholar or central locations in the aggregation.3Kimbell H.S. Morrell L.J. 'Selfish herds' of guppies follow complex movement rules, but not when information is limited.Proc. Biol. Sci. 2015; 282: 20151558Crossref PubMed Scopus (12) Google Scholar, 4Viscido S.V. Wethey D.S. Quantitative analysis of fiddler crab flock movement: evidence for 'selfish herd' behaviour.Anim. Behav. 2002; 63: 735-741Crossref Scopus (77) Google Scholar, 5King A.J. Wilson A.M. Wilshin S.D. Lowe J. Haddadi H. Hailes S. Morton A.J. Selfish-herd behaviour of sheep under threat.Curr. Biol. 2012; 22: R561-R562Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar Alternatively, increased alignment with their neighbors' orientation could reduce the chance of predation through information sharing6Wood A.J. Ackland G.J. Evolving the selfish herd: emergence of distinct aggregating strategies in an individual-based model.Proc. Biol. Sci. 2007; 274: 1637-1642Crossref PubMed Scopus (116) Google Scholar, 7Herbert-Read J.E. Buhl J. Hu F. Ward A.J.W. Sumpter D.J.T. Initiation and spread of escape waves within animal groups.R. Soc. Open Sci. 2015; 2: 140355Crossref PubMed Scopus (68) Google Scholar, 8Sumpter D.J.T. Szorkovszky A. Kotrschal A. Kolm N. Herbert-Read J.E. Using activity and sociability to characterize collective motion.Philos. Trans. R. Soc. Lond. B Biol. Sci. 2018; 373: 20170015Crossref PubMed Scopus (17) Google Scholar or collective escape.6Wood A.J. Ackland G.J. Evolving the selfish herd: emergence of distinct aggregating strategies in an individual-based model.Proc. Biol. Sci. 2007; 274: 1637-1642Crossref PubMed Scopus (116) Google Scholar Using both small and large flocks of homing pigeons (Columba livia; n = 8–10 or n = 27–34 individuals) tagged with 5-Hz GPS loggers and a GPS-tagged, remote-controlled model peregrine falcon (Falco peregrinus), we tested whether individuals increase their use of attraction over alignment when under perceived threat. We conducted n = 27 flights in treatment conditions, chased by the robotic "predator," and n = 16 flights in control conditions (not chased). Despite responding strongly to the RobotFalcon—by turning away from its flight direction—individuals in treatment flocks demonstrated no increased attraction compared with control flocks, and this result held across both flock sizes. We suggest that mutualistic alignment is more advantageous than selfish attraction in groups with a high coincidence of individual and collective interests (adaptive hypothesis). However, we also explore alternative explanations, such as high cognitive demand under threat and collision avoidance (mechanistic hypotheses). We conclude that selfish herd may not be an appropriate paradigm for understanding the function of highly synchronous collective motion, as observed in bird flocks and perhaps also fish shoals and highly aligned mammal aggregations, such as moving herds.