Flocking behaviour in the twilight ascents of Common Swifts Apus apus

Cecilia Nilsson, Johan Bäckman, Adriaan M. Dokter

Research output: Contribution to journalArticlepeer-review


Among the many unique flight behaviours of Common Swifts Apus apus, the most puzzling may be their ascents to high altitudes during both dusk and dawn. Twilight ascents have been hypothesized to be functionally related to information acquisition, including integration of celestial orientation cues, high-altitude visual landmarks and sampling of weather conditions. However, their exact purpose remains unknown. We tracked Common Swifts with tracking radar at their breeding grounds in southern Sweden, and present evidence that during the dusk ascent and dawn descent they often occur in flocks, whereas during the dusk descent and dawn ascent phase they do not. This flocking behaviour suggests that swifts may benefit from conspecific interactions during twilight ascents and descents, possibly through more robust cue acquisition and information exchange in groups, or extending social behaviour also seen in screaming parties before dusk.

Original languageEnglish
Pages (from-to)674-678
Issue number3
Early online date2019 Jan 12
Publication statusPublished - 2019

Subject classification (UKÄ)

  • Zoology
  • Evolutionary Biology


  • flight altitude
  • flight behaviour
  • screaming parties


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