Researchers identify immune cells that could function as an internal compass
Pigeons May Sense Earth’s Magnetic Field in the Liver
- von Juliana Fischer
- 29.05.2026
How pigeons manage to find their way home over hundreds of kilometres has long fascinated scientists. Researchers have known for decades that the birds use the Earth’s magnetic field for orientation — but how exactly they sense it has remained one of biology’s great unanswered questions. A new study published in Science now points to a surprising location: the liver. The research describes specialised immune cells that may be capable of detecting magnetic fields and helping birds navigate. The interdisciplinary study involved physicist Professor Ulf Wiedwald from the University of Duisburg-Essen.
It has long been established that migratory birds and homing pigeons use the Earth’s magnetic field for navigation. However, where this magnetic sense is located and how the signals are processed has remained unclear. Previous hypotheses focused on light-dependent mechanisms in the eye or magnetic particles in the beak, but conclusive experimental evidence has so far been lacking.
The new study in Science* now proposes a different possible mechanism for magnetic perception. At the centre of the research are macrophages — immune cells that store iron while breaking down old red blood cells and therefore play an important role in vertebrate iron metabolism.
To investigate whether iron-containing immune cells are involved in pigeons’ magnetic perception, the team led by physicist Professor Ulf Wiedwald analysed the animals’ eyes, beaks, brains, livers and spleens using highly sensitive magnetic measurement techniques.
“By far the strongest magnetic response was found in the liver, while other tissues showed no comparable signals,” says Ulf Wiedwald. “In liver tissue, iron occurs in crystalline oxide nanoparticles. These give the cells superparamagnetic properties and could make them sensitive to magnetic fields.”
The importance of these cells for orientation was demonstrated in behavioural field experiments with homing pigeons. The ornithological research team trained the birds to return to their aviary at the Max Planck Institute in Radolfzell on Lake Constance from a distance of twenty kilometres. When the iron-containing macrophages were temporarily deactivated using an inhibitory substance, pigeons lost their sense of direction on overcast days when the sun was obscured. In sunny conditions, however, they remained capable of orienting themselves — presumably because they could also use the position of the sun for navigation.
It is still unclear how signals from the liver are transmitted to the brain. However, microscopic images of liver tissue suggest that the cells in question are located in close proximity to nerve fibres. Beyond birds, these findings could also have implications for animals such as sharks, which navigate without light.
* The study brought together the expertise of an interdisciplinary team comprising immunologists from the University of Bonn, physicists from the University of Duisburg-Essen and biologists from the Max Planck Institute of Animal Behavior.
Further Information
Image Caption: Homing pigeons without macrophages navigated successfully home on sunny days (orange), but not on overcast days (blue).
Read the full Press Release at Max Planck Institute of Animal Behaviour:
https://www.ab.mpg.de/944599/news_publication_26511515_transferred
Full Citation: Clivia Lisowski et al., “Homing pigeon navigation relies on superparamagnetic macrophages under overcast conditions,” in *Science*, 2026, DOI: https://doi.org/10.1126/science.ady2486
Professor Ulf Wiedwald, University of Duisburg-Essen, Faculty of Physics, ulf.wiedwald@uni-due.de