德国University of Bonn与Max Planck Institute of Animal Behaviour的科学家发现，鸽子肝脏中的富铁免疫细胞可作为体内指南针，帮助牠们感知地球磁场。研究指出，这些巨噬细胞在分解旧红血球时累积铁，并含有铁蛋白 ferritin，对外界磁场的微小变化极为敏感，为鸟类导航中的「直觉」提供了物理基础。

研究团队先在鸽子体内筛查磁反应最强的器官，结果显示肝脏最突出；进一步分析确认巨噬细胞是关键细胞。当研究人员用 clodronate 清除肝脏巨噬细胞后，追踪显示鸽子在阴天会失去方向感并随机飞行，但在无云晴天仍可借助太阳成功导航，显示磁感与其他线索并行使用。

电子显微镜还发现，肝脏中的神经纤维紧邻这些巨噬细胞，暗示磁讯号可经由肝脏传到大脑。研究者指出，这是首批直接证据，说明地球磁场如何在体内被感知并转化为行动；同时，Oxford University 的 Christiane Timmel 也提到另一条可能路径，即眼睛中的 cryptochrome 透过自由基反应让动物「看见」磁场，显示多重机制可能依情境共同作用。

Scientists from the University of Bonn and the Max Planck Institute of Animal Behaviour found that iron-rich immune cells in pigeons’ livers can act as an internal compass, helping the birds detect Earth’s magnetic field. The key cells are macrophages, which accumulate iron while breaking down old red blood cells and contain ferritin, making them highly sensitive to tiny changes in the external field.

The team first screened pigeons’ bodies for the strongest magnetic response and found the liver stood out. When clodronate was used to remove liver macrophages, homing pigeons lost direction in overcast weather and flew randomly, but they still navigated successfully on cloudless days by using the sun, showing that magnetic sensing works alongside other cues.

Electron microscopy showed nerve fibres running past the macrophages, suggesting a route by which magnetic signals could reach the brain. The researchers said this is the first concrete evidence for how Earth’s magnetic field may be perceived inside the body and translated into movement. Other scientists, including Christiane Timmel, pointed to an alternative eye-based mechanism involving cryptochrome, implying multiple complementary systems may operate depending on the situation.