Department für Geo- und Umweltwissenschaften, Ludwig-Maximillians-Universität München, Theresienstrasse 41/IV, D-80333 Munich, Germany.
Proc Biol Sci. 2013 May 29;280(1763):20130853. doi: 10.1098/rspb.2013.0853. Print 2013 Jul 22.
The avian magnetic compass works in a fairly narrow functional window around the intensity of the local geomagnetic field, but adjusts to intensities outside this range when birds experience these new intensities for a certain time. In the past, the geomagnetic field has often been much weaker than at present. To find out whether birds can obtain directional information from a weak magnetic field, we studied spontaneous orientation preferences of migratory robins in a 4 µT field (i.e. a field of less than 10 per cent of the local intensity of 47 µT). Birds can adjust to this low intensity: they turned out to be disoriented under 4 µT after a pre-exposure time of 8 h to 4 µT, but were able to orient in this field after a total exposure time of 17 h. This demonstrates a considerable plasticity of the avian magnetic compass. Orientation in the 4 µT field was not affected by local anaesthesia of the upper beak, but was disrupted by a radiofrequency magnetic field of 1.315 MHz, 480 nT, suggesting that a radical-pair mechanism still provides the directional information in the low magnetic field. This is in agreement with the idea that the avian magnetic compass may have developed already in the Mesozoic in the common ancestor of modern birds.
鸟类的磁罗盘在当地地磁场强度的相当窄的功能窗口内工作，但当鸟类在一定时间内经历这些新的强度时，它会调整到超出此范围的强度。过去，地磁场通常比现在弱得多。为了弄清楚鸟类是否可以从弱磁场中获得方向信息，我们在 4 µT 磁场中（即磁场强度小于 47 µT 的当地强度的 10%）研究了候鸟知更鸟的自发取向偏好。鸟类可以适应这种低强度：在 4 µT 下，经过 8 小时的预暴露后，它们会出现定向障碍，但在总共 17 小时的暴露后，它们能够在该磁场中定向。这表明鸟类的磁罗盘具有相当大的可塑性。在 4 µT 磁场中的定向不受上喙局部麻醉的影响，但会被 1.315 MHz、480 nT 的射频磁场破坏，这表明自由基对机制仍然提供了低磁场中的方向信息。这与鸟类磁罗盘可能已经在中生代现代鸟类的共同祖先中发展起来的观点一致。
