Magnetic Field May Be a Map for Migratory Birds

磁场是候鸟的地图

撰文/播音  Christopher Intagliata 

翻译  张旭阳

审校  王娇娇

It's well known birds can use Earth's magnetic field as their compass, but they may also use magnetism as their map. Christopher Intagliata reports

众所周知，地球磁场是鸟类的罗盘，然而它可能还是鸟类的地图。

If you're lost, you need a map and a compass. The map pinpoints where you are, and the compass orients you in the right direction. Migratory birds, on the other hand, can traverse entire hemispheres and end up just a couple miles from where they bred last year, using their senses alone. Their compass is the sun, the stars and the Earth's magnetic field. But their map is a little more mysterious. One theory goes that they use olfactory cues—how a place smells. Another is that they rely on their sense of magnetism.

如果你迷路了，你需要地图和罗盘——地图指示位置，罗盘指明方向。然而，候鸟可以穿越整个半球，仅仅凭感觉就能回到去年繁殖地点附近——误差仅仅几英里。它们的罗盘是太阳、群星和地球磁场。但是，它们的地图是什么？这似乎还有些神秘。一种理论认为，各个地方的气味是候鸟定位的线索。另一种理论认为，它们依靠对磁场的感觉来定位。

Researchers in Russia investigated the map issue in a past study by capturing Eurasian reed warblers on the Baltic Sea as they flew northeast towards their breeding grounds near Saint Petersburg. They moved the birds 600 miles east, near Moscow. And the birds just reoriented themselves to the northwest—correctly determining their new position.

在过去的研究中，俄罗斯的研究人员通过在波罗的海捕捉欧亚芦苇莺来调查地图之谜，这些候鸟正在向东北方迁徙，前往圣彼得堡附近的繁殖区。研究人员将这些鸟向东运输了600英里，运到莫斯科附近。鸟群重新调整，开始向西北飞行——它们很正确地判断出了目前的位置。

Trumpeter swans at the Riverlands Migratory Bird Sanctuary in Illinois. Source: U.S. Army Corps of Engineers/Flickr

伊利诺斯州河间地候鸟保护区的喇叭天鹅。图片来源：U.S. Army Corps of Engineers/Flickr

Now the same scientists have repeated that experiment—only this time, they didn't move the birds at all. They just put them in cages that simulated the magnetic field of Moscow, while still allowing the birds to experience the sun, stars and smells of the Baltic. Once again, the birds re-oriented themselves to the northwest—suggesting that the magnetic field alone—regardless of smells or other cues, is enough to alter the birds' mental map. The study is in the journal Current Biology. [Dmitry Kishkinev et al, Eurasian reed warblers compensate for virtual magnetic displacement]

现在，同一批科学家又对这项实验进行了重复——只是这一次，他们并没有运走鸟群。研究人员将鸟群放进模拟莫斯科磁场的笼子中，同时仍然允许它们感受太阳、群星和 波罗的海的气息。又一次，鸟群调整航向，向西北飞行——这表示，抛却气味等其他线索，鸟类仅凭磁场就可以实现定位。这项研究发表在杂志《当代生物学》（Current Biology）上。[Dmitry Kishkinev et al, Eurasian reed warblers compensate for virtual magnetic displacement]

And if you're envious of that sixth sense—keep in mind that since the Earth's magnetic field fluctuates, the researchers say magnetic route-finding is best for crude navigation. Meaning for door-to-door directions—you’re still better off with your GPS.

如果你羡慕这种第六感，一定要记住，因为地球磁场存在波动，研究人员表示通过磁场确定航线最适用于粗略的航行。所以，对于门对门级别的导航，你最好还是带上GPS吧。