How pigeons find their way home over long distances

Research has shown that pigeons’ ability to return home after long flights may be linked not only to their brains or vision, but also to the function of their liver. Recent scientific findings suggest that immune cells in the pigeons’ liver can sense the Earth's magnetic field, providing the birds with an internal compass.

The role of magnetoreception in bird navigation

For many years, it has been known that migratory and homing birds partially navigate using the geomagnetic field, especially when other cues like the sun or stars are unavailable. Magnetoreception helps birds determine their location and choose a direction, but the exact mechanisms behind this process have long remained unclear. Various hypotheses have been proposed, including the possibility that birds sense magnetic fields through light-sensitive molecules in their eyes or magnetic particles in their beaks, but none of these theories have been definitively proven by experiments.

New insights into magnetoreception mechanisms

In a recent study published in the journal Science, researchers explored an alternative mechanism. They discovered that macrophages—immune cells found in the pigeons’ liver—possess magnetic properties. Similar properties had previously been observed in the macrophages of mice and humans, where they are associated with iron accumulation during the breakdown of red blood cells. In pigeons, iron accumulates in macrophages as ferritin nanocapsules, allowing the iron to be stored in a non-toxic form.

To test for magnetic properties in pigeon tissues, the researchers used vibrational magnetometry and magnetic cell separation techniques, analyzing various organs including the beak, muscles, brain, eyes, spleen, and liver. The highest concentration of iron was found in the liver, and the liver’s macrophages showed the greatest sensitivity to magnetic fields.

Experimental confirmation

In experiments with pigeons trained to return home from distances of over 20 kilometers, it was found that on cloudy days, when the sun was hidden, birds whose liver macrophages had been removed lost their sense of direction. On sunny days, these pigeons were able to navigate successfully by using the sun as a guide. These results confirmed that the liver and its immune cells help pigeons perceive the geomagnetic field and maintain their direction when other cues are absent.

Signal transmission to the brain

Further research revealed that iron-containing liver macrophages are located near nerve fibers, which likely serve as pathways for transmitting information to the brain. This discovery points to a previously unknown mechanism for magnetic field perception in animals and provides the first concrete evidence that the Earth's magnetic field can be detected by the body and relayed to the brain to guide movement.