How pigeons exploit magnetic fields for navigation

鸽子如何利用磁场进行导航

Scientists have long known that migrating birds and homing pigeons navigate in part by sensing the Earth’s magnetic fields, especially at night or in overcast conditions when visual landmarks or sunshine are in short supply. But exactly where this magneto-sensing occurs in the body—and the mechanism that enables it—remains a matter of intense debate. 科学家们早就知道，候鸟和信鸽在一定程度上是通过感知地球磁场来导航的，尤其是在夜间或阴天、缺乏视觉地标或阳光的情况下。但这种磁感应究竟发生在身体的哪个部位，以及实现这一功能的机制是什么，仍然是一个激烈争论的话题。

A new paper published in the journal Science suggests that homing pigeons have iron-rich immune cells in their livers that help them detect magnetic fields and transmit that information to the brain. 发表在《科学》杂志上的一篇新论文指出，信鸽的肝脏中含有富含铁的免疫细胞，这些细胞能帮助它们探测磁场并将信息传递给大脑。

There are three primary hypotheses for how birds might sense Earth’s geomagnetic field. One is a compass-like mechanism, whereby the Earth exerts a pull on magnetic particles in a bird’s upper beak that relays directional information via a large nerve in the cranium. A second is that it happens biologically via cellular ion channels sensitive to voltage, enabling birds to sense changes in the magnetic field. And a third suggests that physical effects on retinal pigments enable birds to detect photons and send signals to the brain, although this mechanism is really only viable in the light. None fully explain how animals can sense magnetic fields. 关于鸟类如何感知地球地磁场，目前有三种主要假说。第一种是类似指南针的机制，即地球对鸟类上喙中的磁性颗粒产生拉力，并通过颅内的一条大神经传递方向信息。第二种是通过对电压敏感的细胞离子通道进行生物学感知，使鸟类能够感知磁场的变化。第三种认为，视网膜色素的物理效应使鸟类能够探测光子并向大脑发送信号，尽管这种机制实际上只有在有光的情况下才可行。目前还没有哪种假说能完全解释动物是如何感知磁场的。

However, “We had some clues that the liver and spleen have magnetic properties, because they break down red blood cells and so store much iron in the body,” said co-author Clivia Lisowski of the University of Bonn and the University Hospital Bonn. This refers to a 2015 paper suggesting that red pulp macrophages in the spleens of mice and humans are intrinsically superparamagnetic and hence more sensitive to magnetic fields. But it wasn’t clear if those properties were involved in any kind of magnetoreception. 然而，波恩大学和波恩大学医院的合著者克利维亚·利索夫斯基（Clivia Lisowski）表示：“我们有一些线索表明肝脏和脾脏具有磁性，因为它们分解红细胞，因此在体内储存了大量铁。”这指的是2015年的一篇论文，该论文指出小鼠和人类脾脏中的红髓巨噬细胞本质上是超顺磁性的，因此对磁场更敏感。但目前尚不清楚这些特性是否参与了任何形式的磁感应。

For their homing pigeon study, Lisowski et al. used vibrating sample magnetometry and magnetic cell separation to test liver and spleen tissue samples stained with Prussian blue—which is sensitive to ferritin, a red blood cell degradation product—along with the eyes, beak, and brain. They found the strongest concentration of iron and the strongest magnetic response in the liver tissue. 在信鸽研究中，利索夫斯基等人使用了振动样品磁强计和磁性细胞分离技术，对用普鲁士蓝染色（对红细胞降解产物铁蛋白敏感）的肝脏和脾脏组织样本，以及眼睛、喙和大脑进行了测试。他们发现肝脏组织中的铁浓度最高，磁响应也最强。

An internal compass

内置指南针

To further test their hypothesis, Lisowski et al. trained 34 pigeons to home over a west-to-east route covering 19 kilometers (just under 12 miles). Once trained, half the birds were injected with clodronate liposomes to deplete macrophages in the liver, while the other half served as a control group. This was done the day before weather predictions called for overcast conditions with the sun obscured. The next day, all the pigeons were released. 为了进一步验证他们的假设，利索夫斯基等人训练了34只信鸽，让它们沿一条19公里（不到12英里）的西向东路线归巢。训练完成后，一半的鸽子被注射了氯膦酸盐脂质体以耗尽肝脏中的巨噬细胞，另一半作为对照组。这项操作是在天气预报称会有阴天且阳光被遮挡的前一天进行的。第二天，所有的鸽子被放飞。

All the pigeons in the control group successfully navigated their way back to the aviary; those that received the injections lost their sense of direction and did not return home until the following day, when the sun was out. A follow-up experiment with the clodronate-treated pigeons under sunny conditions did not affect their homing ability because they were able to use solar cues. This suggests that pigeons use a combination of the sun’s orientation and magnetic sensing to navigate—and the latter is a previously unsuspected mechanism for magnetic perception in animals. 对照组的所有鸽子都成功导航回到了鸽舍；而接受注射的鸽子则失去了方向感，直到第二天阳光出来后才回到家。在阳光充足的条件下对接受氯膦酸盐处理的鸽子进行的后续实验显示，它们的归巢能力并未受到影响，因为它们能够利用太阳线索。这表明鸽子是结合太阳方位和磁感应来进行导航的——而后者是动物磁感知中一种此前未被怀疑的机制。

The authors think these results could also explain magnetoreception in bats and blind mole rats, which don’t have functioning cryptochromes or live in environments with little to no light. They might also apply to certain species of shark capable of swimming in straight lines over long distances—such as scalloped hammerhead sharks, which seem to orient themselves using seamounts found to have geomagnetic anomalies. 作者认为，这些结果也可以解释蝙蝠和盲鼹鼠的磁感应能力，它们要么没有功能性的隐花色素，要么生活在几乎没有光线的环境中。这些发现也可能适用于某些能够长距离直线游动的鲨鱼，例如扇头双髻鲨，它们似乎利用具有地磁异常的海山来定位。

“Beyond magneto reception, our findings contribute to a broader emerging concept: tissue-resident macrophages can function as peripheral sensory cells, providing direct, biologically meaningful feedback to the brain,” the authors concluded. 作者总结道：“除了磁感应之外，我们的发现还促成了一个更广泛的新兴概念：组织驻留巨噬细胞可以作为外周感觉细胞，向大脑提供直接的、具有生物学意义的反馈。”

In an accompanying perspective, Simon Spiro of the Zoological Society of London and Hal Drakesmith of the University of Oxford noted some caveats. For instance, the iron-rich cells in the liver could have been due to the diet of captive pigeons, given that many zoo-housed animals have iron overloads. They also don’t think it’s yet clear that the liver is the best and most likely organ for sensing magnetic fields. It’s possible that doping the pigeons with clodronate also depleted macrophages located elsewhere in the body, skewing the histological results. 在随附的评论文章中，伦敦动物学会的西蒙·斯皮罗（Simon Spiro）和牛津大学的哈尔·德雷克斯史密斯（Hal Drakesmith）指出了几点注意事项。例如，肝脏中富含铁的细胞可能是由于圈养鸽子的饮食造成的，因为许多动物园饲养的动物都存在铁过载问题。他们还认为，目前尚不清楚肝脏是否是感知磁场最好、最可能的器官。给鸽子注射氯膦酸盐也可能耗尽了身体其他部位的巨噬细胞，从而扭曲了组织学结果。

Spiro and Drakesmith cite a 2025 study, also published in Science, that used a different, more global methodology and suggested a different mechanism: Special cells within the pigeon forebrain encode magnetic information, thereby facilitating effective navigation. Both potential mechanisms do not require light stimulation, so it’s possible there could be… 斯皮罗和德雷克斯史密斯引用了同样发表在《科学》杂志上的另一项2025年的研究，该研究使用了不同且更全面的方法，并提出了另一种机制：信鸽前脑内的特殊细胞对磁信息进行编码，从而促进有效的导航。这两种潜在机制都不需要光刺激，因此有可能存在……