Damping of waves of agitation in starling flocks

C. K. Hemelrijk*, A. Costanzo, H. Hildenbrandt, C. Carere

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

When a predator attacks a flock of starlings (Sturnus vulgaris), involving thousands of individuals, a typical collective escape response is the so-called agitation wave, consisting of one or more dark bands (pulses) propagating through the flock and moving away from the predator (usually a Peregrine falcon, Falco peregrinus). The mechanism underlying this collective behavior remains debated. A theoretical study has suggested that the individual motion underlying a pulse could be a skitter (in the form of a zigzag), that is copied by nearby neighbors, and causes us to temporarily observe a larger surface of the wing because the bird is banking during turning while zigzagging. It is not known, however, whether pulses during a wave event weaken over time. This is of interest, because whereas during the usual turning by an undisturbed flock the motion is copied completely without weakening, we may expect that pulses dampen during a wave event because individuals that are further away from a predator react less because of reduced fear. In the present paper, we show in empirical data that pulses during a wave event weaken over time. Our computational model, StarDisplay, reveals that this is most likely a consequence of a reduction of the maximum banking angle during the zigzag escape maneuver rather than by a reduced tendency to copy this maneuver with time. The response seems adaptive because of lowered danger at a larger distance to the location of attack.

Original languageEnglish
Article number125
Number of pages7
JournalBehavioral Ecology and Sociobiology
Volume73
Issue number9
DOIs
Publication statusPublished - Sep-2019

Keywords

  • Flocking
  • Starling
  • Predation
  • Agitation wave
  • Collective escape
  • Zigzag
  • STURNUS-VULGARIS
  • PREDATION
  • PATTERNS
  • SCHOOLS
  • SHAPE
  • FISH
  • PREY

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