Published on 5/31/2026
For decades, scientists have known that birds do not rely on just one sense to migrate. They use the sun when the sky is clear, and benefit from smells, visual landmarks, and previous experience with the route. They can also use the stars. But on cloudy days, when the sun disappears and visual signs weaken, a more mysterious ability emerges: sensing the Earth’s magnetic field.
This sense, known as “magnetic perception,” is one of the most controversial animal senses in research circles, as its effects have been observed in migratory birds, sea turtles, sharks, and perhaps some mammals. Scientists have always asked about the location of the biocompass inside the body, and how the invisible magnetic field lines are transformed into a neural signal that the brain understands.
One answer to this question appears in a new study published in the journal Science that suggests an unexpected answer, which is that this compass is found in the liver, specifically within iron-rich immune cells called macrophages.
From immunity to navigation
cells Macrophages It is known for its role in cleaning the body, as it devours dead cells, and participates in dismantling old red blood cells, so it was not strange that it contains iron compounds, and therefore these cells, according to the new study, may be able to perform a sensory function, which is to capture information from the Earth’s magnetic field.
According to the study, scientists examined various tissues of passenger pigeons, looking for magnetic signals. It was expected that the strongest signal would appear in the spleen, because in mammals it is a major organ in recycling blood cells, but the surprise came from the liver, as it showed the strongest magnetic response among the tissues examined.
When examining fine slices of pigeon liver, the researchers found that certain phagocytic cells contain high concentrations of iron, and that they are located near nerve fibers. This proximity is very important; Because it opens the possibility that these cells, if they respond to the magnetic field, transmit their signals to the nervous system, and from there to the brain.
Not only did the researchers show the presence of iron-rich cells in the liver, but they also tried to test whether they were actually necessary for navigation. The team trained 34 carrier pigeons to return from a distance of approximately 19 kilometers.
Under normal circumstances, pigeons can use the position of the sun to determine direction, but when the sky is completely overcast, relying on the sun becomes difficult, and here the importance of the magnetic sense increases.
The researchers injected 18 pigeons with a substance used to remove macrophages from the body, then released them on a cloudy day in which the sun was completely blocked. The result was remarkable, as the birds lost their way and did not return until conditions improved and other navigational signs appeared. In contrast, the birds that received sham injections returned to their homes normally.
To ensure that the injected substance did not make the birds ill or generally disoriented, the researchers released pigeons treated in the same way on sunny days. The birds then returned successfully, indicating that the problem was not general flight ability or motivation to return, but rather navigation ability when the sun went down and the magnetic compass became more important.
The hypothesis proposed by the researchers is that iron particles inside macrophages may possess precise magnetic properties that make them affected by the direction of the magnetic field. When the bird changes the direction of its body relative to the Earth’s field lines, the response of these particles may change, affecting the internal structure of the cell or chemical signals close to the nerve fibers.
Caution is a must
Despite the important results, the study does not completely resolve the puzzle, as there are still big questions about the amount of iron in macrophages that is required to produce a measurable response to the Earth’s weak magnetic field.
Some researchers also expressed clear skepticism, not because the behavioral results are not important, but because the history of this field is full of hypotheses that seemed promising but then declined in the face of subsequent tests.
Therefore, critics say, the next step should not be limited to removing the cells and monitoring the loss of birds, but should include manipulating the magnetic information itself and seeing whether the bird can be guided or misled in a predictable way.
This caution does not diminish the value of the study, but rather puts it in its rightful place: a powerful and exciting step, but it requires additional experiments before a final solution to one of the most complex mysteries of animal senses can be announced.
