Study type: Medical/biological study (experimental study)

Not all songbirds calibrate their magnetic compass from twilight cues: a telemetry study med./bio.

Published in: J Exp Biol 2011; 214 Pt 15: 2540-2543

Aim of study (acc. to author)

Migratory birds are able to use the sun and associated polarised light patterns, stellar cues and the geomagnetic field for orientation. No general agreement has been reached regarding the hierarchy of orientation cues.
In this study the hypothesis was tested, 1) whether the magnetic compass is calibrated from twilight celestial cues, 2) either magnetic or stellar cues are used separately without transferring reference information to others (simple domination) or 3) whether the stellar compass is calibrated from the magnetic field.

Background/further details

All song thrushes were captured during the autumn and spring passage in Rybachy, Kaliningrad Region, Russia. In autumn, only hatching-year birds were tested and in spring, only second calendar year birds were included. Birds were released at two different locations to test whether they used landmarks or global cues (solar, stellar or geomagnetic). All birds were radio tagged and could be followed for at least 15 km. Birds were exposed one hour before sunset and released when the sun was 12° below the horizon.

Endpoint

Exposure

Exposure Parameters
Exposure 1:
  • unspecified
Exposure duration: continuous for 1 h
-

Exposure 1

Main characteristics
Frequency
  • unspecified
Type
Exposure duration continuous for 1 h
Exposure setup
Exposure source
Setup cuboid coil with 1m side length; cage placed in the center of the coil system; magnetic field in this area uniform; magnetic field horizontally rotated; exposure system placed outdoors
Sham exposure A sham exposure was conducted.
Additional info for autumn experiments magnetic field deflected 120° clockwise, for spring experiments magnetic field deflected 120° anticlockwise
Parameters

No parameters are specified for this exposure.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

The song thrushes chose a seasonally appropriate migratory direction regardless of whether they had been exposed to the magnetic field prior to release or not, both in autumn and spring. The hypothesis that song thrushes calibrate their magnetic compass from celestial twilight cues is not supported; instead, the hypothesis of the magnetic or stellar compass dominating is confirmed.
The authors suggest that different songbird species possess different hierarchies of orientation cues, depending on the geographic and ecological challenges met by the migrants.

Study character:

Study funded by

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