How do pigeons find their way home safely over distances of many kilometers? A research team from the University Hospital Bonn (UKB), the University of Bonn, the University of Duisburg-Essen, and the Max Planck Institute for Behavioral Biology has now discovered a previously unknown mechanism: specific immune cells in the liver may help the birds detect the Earth’s magnetic field. The findings have now been published in the journal Science.
The study focuses on so-called macrophages. These immune cells, among other things, break down old red blood cells and store iron nanoparticles in the process. This stored iron gives the cells magnetic properties. The researchers observed that carrier pigeons exhibited impaired orientation under overcast skies when the function of these iron-rich immune cells was compromised. When the sun was visible, the birds continued to find their way back and apparently used visual cues for orientation.
“Our results reveal a previously unknown mechanism of magnetic perception in animals,” says Prof. Christian Kurts, Director of the Institute for Molecular Medicine and Experimental Immunology at the UKB and a member of the TRA Life and Health at the University of Bonn. “The fact that immune cells could act as sensors for magnetic fields surprised even us.”
To track down the magnetically active cells, the team examined various organs of the animals, including the eyes, beak, brain, liver, and spleen. The liver, in particular, showed a high concentration of superparamagnetic iron particles. Further analyses identified macrophages as the key cell population.
“Of all the tissues examined, the liver exhibited the strongest magnetic properties,” explains lead author Dr. Clivia Lisowski of the Institute of Molecular Medicine and Experimental Immunology at the UKB. “Our data provide the first concrete evidence of how the Earth’s magnetic field might be detected within the body and transmitted to the brain.”
Electron microscopic examinations also showed that the iron-rich macrophages are located in the immediate vicinity of nerve fibers. This suggests that magnetic information could be transmitted from there to the nervous system.
“Animal navigation is one of the most fascinating phenomena in nature,” says Prof. Dr. Martin Wikelski, Director of the Department of Animal Migration at the Max Planck Institute for Behavioral Biology. “If it is confirmed that immune cells are involved, this would represent a fundamental paradigm shift in our understanding of orientation in the animal kingdom.”
The study thus combines insights from immunology, physics, and behavioral biology and offers a new approach to explaining animal navigation. The researchers suspect that similar mechanisms may also occur in other animal species.
Participating institutions and funding
The research was funded by, among others, the German Research Foundation (DFG), the Max Planck Society, and the Gordon and Betty Moore Foundation.
Publication
Clivia Lisowski et al., “Homing pigeon navigation relies on superparamagnetic macrophages under overcast conditions,” in Science, 2025, DOI: 10.1126/science.ady2486
Contact
Dr. Clivia Lisowski
Institute for Molecular Medicine and Experimental Immunology at the UKB
Email: cliso@uni-bonn.de
Prof. Christian Kurts
Institute for Molecular Medicine and Experimental Immunology at the UKB
Member of the Transdisciplinary Research Area (TRA) Life and Health at the University of Bonn
Email: ckurts@uni-bonn.de
