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Confronting the winds: orientation and flight behaviour of roosting swifts, Apus apus

Bäckman, Johan LU and Alerstam, Thomas LU (2001) In Royal Society of London. Proceedings B. Biological Sciences 268(1471). p.1081-1087
Abstract
Swifts, Apus apus, spend the night aloft and this offers an opportunity to test the degree of adaptability of bird orientation and flight to different ecological situations. We predicted the swifts' behaviour by assuming that they are adapted to minimize energy expenditure during the nocturnal flight and during a compensatory homing flight if they become displaced by wind. We tested the predictions by recording the swifts' altitudes, speeds and directions under different wind conditions with tracking radar; we found an agreement between predictions and observations for orientation behaviour, but not for altitude and speed regulation. The swifts orientated consistently into the head wind, with angular concentration increasing with... (More)
Swifts, Apus apus, spend the night aloft and this offers an opportunity to test the degree of adaptability of bird orientation and flight to different ecological situations. We predicted the swifts' behaviour by assuming that they are adapted to minimize energy expenditure during the nocturnal flight and during a compensatory homing flight if they become displaced by wind. We tested the predictions by recording the swifts' altitudes, speeds and directions under different wind conditions with tracking radar; we found an agreement between predictions and observations for orientation behaviour, but not for altitude and speed regulation. The swifts orientated consistently into the head wind, with angular concentration increasing with increasing wind speed. However, contrary to our predictions, they did not select altitudes with slow or moderate winds, nor did they increase their airspeed distinctly when flying into strong head winds. A possible explanation is that their head-wind orientation is sufficient to keep nocturnal displacement from their home area within tolerable limits, leaving flight altitude to be determined by other factors (correlated with temperature), and airspeed to show only a marginal increase in strong winds. The swifts were often moving 'backwards: heading straight into the wind but being overpowered by wind speeds exceeding their airspeed. The regular occurrence of such flights is probably uniquely associated with the swifts' remarkable habit of roosting on the wing. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Royal Society of London. Proceedings B. Biological Sciences
volume
268
issue
1471
pages
1081 - 1087
publisher
Royal Society
external identifiers
  • scopus:0035932922
ISSN
1471-2954
DOI
10.1098/rspb.2001.1622
language
English
LU publication?
yes
id
c77f91ab-af94-416a-ae27-215718fde311 (old id 145794)
date added to LUP
2007-06-26 07:10:14
date last changed
2018-02-18 03:42:40
@article{c77f91ab-af94-416a-ae27-215718fde311,
  abstract     = {Swifts, Apus apus, spend the night aloft and this offers an opportunity to test the degree of adaptability of bird orientation and flight to different ecological situations. We predicted the swifts' behaviour by assuming that they are adapted to minimize energy expenditure during the nocturnal flight and during a compensatory homing flight if they become displaced by wind. We tested the predictions by recording the swifts' altitudes, speeds and directions under different wind conditions with tracking radar; we found an agreement between predictions and observations for orientation behaviour, but not for altitude and speed regulation. The swifts orientated consistently into the head wind, with angular concentration increasing with increasing wind speed. However, contrary to our predictions, they did not select altitudes with slow or moderate winds, nor did they increase their airspeed distinctly when flying into strong head winds. A possible explanation is that their head-wind orientation is sufficient to keep nocturnal displacement from their home area within tolerable limits, leaving flight altitude to be determined by other factors (correlated with temperature), and airspeed to show only a marginal increase in strong winds. The swifts were often moving 'backwards: heading straight into the wind but being overpowered by wind speeds exceeding their airspeed. The regular occurrence of such flights is probably uniquely associated with the swifts' remarkable habit of roosting on the wing.},
  author       = {Bäckman, Johan and Alerstam, Thomas},
  issn         = {1471-2954},
  language     = {eng},
  number       = {1471},
  pages        = {1081--1087},
  publisher    = {Royal Society},
  series       = {Royal Society of London. Proceedings B. Biological Sciences},
  title        = {Confronting the winds: orientation and flight behaviour of roosting swifts, Apus apus},
  url          = {http://dx.doi.org/10.1098/rspb.2001.1622},
  volume       = {268},
  year         = {2001},
}