この研究は、渡り鳥のオリエンテーションキューの階層に関してさまざまな報告がある中で、北米カタルスツグミに関して最近、報告された研究知見について実験的に検証を行った。その報告では、カタルスツグミは日没後の薄明をキューとして、毎日、地磁気情報を較正することを示唆した。しかし、ケージに入れられたトリでの研究の一部は、この知見を確認し、他の研究は確認しなかった。本研究は、ウタツグミ（Turdus philomelos：ヨーロッパの渡り鳥の一種）を放鳥する前に、水平に回転する磁界への事前ばく露を行い、その後、自由に飛行させて観察した。その結果、自由飛行するウタツグミは、太陽のキューで磁気コンパスを再較正せず、磁気コンパスまたは恒星コンパスのどちらかが単純に優勢であることを示した；渡り鳥にとっての地理的および生態学的な制約の下、渡り鳥の種はそれぞれに異なるオリエンテーションキューの階層を持つことが示唆された、と報告している。
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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.
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.
| ばく露 | パラメータ |
|---|---|
ばく露1:
ばく露時間:
continuous for 1 h
|
- |
| 周波数 |
|
|---|---|
| タイプ |
|
| ばく露時間 | continuous for 1 h |
| ばく露の発生源／構造 | |
|---|---|
| ばく露装置の詳細 | 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 information | for autumn experiments magnetic field deflected 120° clockwise, for spring experiments magnetic field deflected 120° anticlockwise |
No parameters are specified for this exposure.
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.
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