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Twilight ascents by common swifts, Apus apus, at dawn and dusk: acquisition of orientation cues?

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Author

  • Adriaan M. Dokter
  • Susanne Åkesson
  • Hans Beekhuis
  • Willem Bouten
  • Luit Buurma
  • Hans van Gasteren
  • Iwan Holleman

Summary, in English

Common swifts are specialist flyers spending most of their life aloft, including night-time periods when this species roosts on the wing. Nocturnal roosting is preceded by a vertical ascent in twilight conditions towards altitudes of up to 2.5 km, behaviour previously explained as flight altitude selection for sleeping. We examined the nocturnal flight behaviour of swifts, as uniquely identified by a Doppler weather radar in central Netherlands using continuous measurements during two consecutive breeding seasons. Common swifts performed twilight ascents not only at dusk but also at dawn, which casts new light on the purpose of these ascents. Dusk and dawn ascents were mirror images of each other when time-referenced to the moment of sunset and sunrise, suggesting that the acquisition of twilight-specific light-based cues plays an important role in the progression of the ascents. Ascent height was well explained by the altitude of the 280 K isotherm, and was not significantly related to wind, cloud base height, humidity or the presence of nocturnal insects. We hypothesize that swifts profile the state of the atmospheric boundary layer during twilight ascents and/or attempt to maximize their perceptual range for visual access to distant horizontal landmarks, including surrounding weather. We compare twilight profiling by swifts with vertical twilight movements observed in other taxa, proposed to be related to orientation and navigation. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Publishing year

2013

Language

English

Pages

545-552

Publication/Series

Animal Behaviour

Volume

85

Issue

3

Document type

Journal article

Publisher

Elsevier

Topic

  • Biological Sciences

Keywords

  • Apus apus
  • atmospheric assessment
  • celestial cue
  • common swift
  • flight
  • altitude
  • orientation
  • navigation
  • twilight
  • weather radar

Status

Published

Research group

  • Animal Navigation Lab

ISBN/ISSN/Other

  • ISSN: 1095-8282