QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bäckman, J. Articles by Alerstam, T. Search for Related Content PubMed PubMed Citation Articles by Bäckman, J. Articles by Alerstam, T.

The Journal of Experimental Biology 205, 905-910 (2002)
© 2002 The Company of Biologists Limited

Harmonic oscillatory orientation relative to the wind in nocturnal roosting flights of the swift Apus apus

Johan Bäckman^* and Thomas Alerstam

Department of Animal Ecology, Ecology Building, Lund University, S-22362 Lund, Sweden

^* e-mail: Johan.Backman{at}zooekol.lu.se

Accepted 11 December 2001

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.

Key words: common swift, Apus apus, flight, Fourier transform, harmonic oscillation, orientation, roosting, wind, tracking radar, autocorrelation

This article has been cited by other articles:

				P. Henningsson, G. R. Spedding, and A. Hedenstrom Vortex wake and flight kinematics of a swift in cruising flight in a wind tunnel J. Exp. Biol., March 1, 2008; 211(5): 717 - 730. [Abstract] [Full Text] [PDF]