Harmonic oscillatory orientation relative to the wind in nocturnal roosting flights of the swift Apus apus.
Författare
Summary, in English
Swifts regularly spend the night flying at high altitude. From previous studies based on tracking radar observations, we know that they stay airborne during the night and prefer to orient themselves into the wind direction with an increased angular concentration with increasing wind speed. In this study, we investigated the orientation relative to the wind of individual swifts by frequency (discrete Fourier transform) and autocorrelation analysis based on time series (10s intervals) of the angle between the swifts' heading and the wind direction for radar trackings of long duration (9-60 min). The swifts often showed a significant harmonic oscillation of their heading direction relative to the wind, with a frequency mostly in the range 1-17 mHz, corresponding to cycle periods of 1-16 min. The swifts also sometimes performed circling flights at low wind speeds. Wind speed ranged from 1.3 to 14.8 m s(-1), and we expected to find different patterns of orientation at different wind speeds, assuming that the swifts adapt their orientation to avoid substantial displacement during their nocturnal flights. However, oscillatory orientation was found at all wind speeds with variable frequencies/periods that did not show any consistent relationship with wind speed. It remains to be shown whether cyclic heading changes are a regular feature of bird orientation.
Avdelning/ar
Publiceringsår
2002
Språk
Engelska
Sidor
905-910
Publikation/Tidskrift/Serie
Journal of Experimental Biology
Volym
205
Issue
Pt 7
Fulltext
- Available as PDF - 264 kB
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Länkar
Dokumenttyp
Artikel i tidskrift
Förlag
The Company of Biologists Ltd
Ämne
- Biological Sciences
Status
Published
ISBN/ISSN/Övrigt
- ISSN: 1477-9145