For more than a century, scientists knew that homing pigeons could find their way back to their lofts after traveling hundreds of miles, with no map or landmarks to guide them, yet the mechanism remained a mystery.
The answer, published on May 28, 2026, in the journal Science, came from a place no one anticipated: the liver.
An international team of researchers identified that cells called macrophages accumulate iron when they break down aging red blood cells. This iron gives them magnetic properties, enabling them to respond to Earth’s magnetic field.
The cells are superparamagnetic, meaning they behave like tiny magnets. The researchers propose that the system does not rely on a single cell, but on the collective signal of many macrophages.
Electron microscopy images of liver tissue showed that these iron-laden macrophages are in direct contact with nerve fibers, suggesting how the magnetic signal travels to the brain.
The study began, in part, by accident.
Ornithologist Martin Wikelski, of the Max Planck Institute of Animal Behavior, and immunologist Christian Kurts, of the University of Bonn, crossed paths at a scientific conference.
Kurts mentioned that macrophages in the spleens of mice and humans contained magnetic iron particles that formed when those cells recycled aging red blood cells. Wikelski, who had never fully accepted existing theories of avian magnetic orientation, saw it immediately: that could be the answer.
That conversation sparked more than a decade of collaboration among immunologists, physicists, and ornithologists.
The Proof: Without Macrophages, Pigeons Lose Their Way
The team trained pigeons to navigate a 19-kilometer route in Germany.
When their liver macrophages were removed via an injection of clodronate liposomes, the birds navigated normally on sunny days. Under overcast skies, however, the pigeons without liver macrophages lost their way.
The result points to a dual navigation system: when the sun is visible, pigeons navigate by visual cues; when it is hidden, they fall back on their internal compass.
A Century-Old Debate, an Unexpected Answer
Magnetoreception (the ability to detect and respond to magnetic fields) has sparked controversy in biology for decades.
Experiments in the 1960s had already shown that captive European robins altered their movements in response to artificial magnetic fields, but the underlying biological mechanism remained a mystery.
Mechanisms proposed over the years included proteins in the eyes, particles in the beak, and fluid in the inner ear.
“What seems like instinct in bird navigation may actually have a physical basis,” Wikelski said. “We did not expect immune cells to act as magnetic field sensors.”
“Our results reveal a previously unknown mechanism of magnetic perception in animals,” Kurts added.
The study appeared on the cover of Science and drew immediate responses from the scientific community.
Catherine Lohmann, a sensory ecologist at the University of North Carolina, called the concept “simply astonishing” and noted that it marks an entirely new direction in a debate that has run for decades.
What Still Remains to Be Answered
The authors themselves acknowledge that the mechanism is far from fully understood.
It remains to be determined exactly what happens inside the macrophages to make them sensitive to the magnetic field, which nerves carry that signal to the brain, and which brain regions process the information.
According to Clivia Lisowski, who led the study, these findings provide the first concrete evidence of how Earth’s magnetic field can be detected in the body and transmitted to the brain to guide movement.
But the finding raises an even bigger question: do other animals also use their immune system as a compass, or has evolution solved the problem of magnetoreception in more than one way?
Sea turtles, lobsters, moths, and bats all rely on Earth’s magnetic field to navigate.
What remains to be seen is whether the liver mechanism is unique to pigeons, or a tool the rest of the animal kingdom shares.
