The invisible compass: how pigeons use Earth’s magnetic field to navigate

The ability to sense the environment we are in is the first step to interact and adapt to this ever-changing world. Therefore, animals have evolved sensory systems that can detect many physical properties of the natural world, such as light, sound, temperature, force, et cetera. In Chapter 4 and 6 of Principles of Neurobiology, we have discussed such sensory systems that are familiar and critical for our human experience perceiving the surroundings. Other animals that live in drastically different environments have evolved some unique sensory pathways that allow them to detect different cues from the environment, as introduced in Chapter 13. One of the most fascinating examples is the magnetoception of birds. Many birds migrate over long distances throughout their lifetime for food and mate. Arctic tern, as one of the most extreme examples, migrates annually from the North Pole to the South Pole and travels about 40,000 miles. During long migrations at high altitude, birds often lack clear landmarks for them to orient and make sure they are on the right track. Therefore, magnetic field emerges as a great reference for these animals to position themselves in an allocentric coordinate as the magnetic field remains constant throughout day and night and weather conditions. Despite the clear advantages of magnetoception and behavioral evidence showing that artificial magnetic field could alter birds’ traveling direction, the exact mechanism for how birds detect magnetic fields remain elusive.

Homing pigeons have been a classic model to study bird magnetoception as they can faithfully return to certain locations irrespective of weather or time of the day which recapitulate the navigation skills of migratory birds. There are three hypotheses for pigeon’s magnetoception. First, there are iron-rich cells in the beak which could be used to detect magnetic field, but we lack clear evidence of how such information enters the brain. Second, the cryptochrome molecule in the retina could alter its biophysical properties in the presence of light and magnetic field, which still does not explain why birds can navigate at night. Third, scientists assumed that there are magnetic-sensitive ion channels in the vestibular system which could directly sense magnetic field. However, such ion channels haven’t been found yet.

In a paper published in the journal of Science in May 2026, Lisowski et al. suggested a fourth theory that could explain magnetoception in pigeons. Building on the first aforementioned hypothesis, they embarked on a search for iron-rich cells in the body and found that the liver has highly enriched iron-rich macrophages. These macrophages display above-background ferrimagnetic/superparamagnetic signals which are comparable with the earth’s magnetic field. The molecule within the macrophage that can detect such change is ferritin which contains high level of Fe3+ ions. The researchers theorized that these iron-rich macrophages in the liver are the sensors for magnetic field, but they still need to manipulate these cells to establish casual relationships. To achieve this, they injected the pigeons with clodronate liposome that depleted macrophages and let them perform the homing task under sunny and overcast days. The pigeons are able to return home under sunny conditions but unable to do so under overcast conditions, suggesting that the liver magnetoception can compensate for sun compass–guided navigation and explains how pigeons navigate without visual landmarks. Furthermore, after the clodronate liposome has been metabolized and the macrophages regenerate, the injected pigeons regain their ability to navigate during overcast days. This result partially rebuts potential concerns regarding the animals lost ability to navigate due to broader health impact of the clodronate liposome injection as there is no long-term impact of pigeon’s navigation ability.

What could be the neural pathway that transduce the magnetic signal from macrophages to neural activity to guide pigeons to navigate? The researchers proposed that the vagus nerve, discussed in Chapter 9 of Principles of Neurobiology, can innervate internal organs and send interoceptive information to the brain. Using electron microscope, the scientists found anatomical evidence of vagus nerve afferents in close proximity with the iron-rich macrophages, providing structural evidence for their hypothesis. This intriguing idea shows that the vagal system, or more broad brain-body connections, could serve other functions beside merely passing interoceptive information. As the body is interacting with the surroundings, these brain-body connections could sense external environment through changes in the body. Still, more evidence is needed to demonstrate that these vagus nerve-macrophage connections are actively responding to changes in magnetic field. There are also more questions regarding how the macrophages respond to magnetic field and what information is sent to the vagus nerve. With more work, we will begin to uncover the unconventional ways animals perceive the world, and their unique neural adaptations for their abilities.

Figure 1. Mechanisms for magnetoception in pigeons. (A) Illustration of how liver macrophages detects magnetic field. (B) Ferric ion presence in different pigeon tissues. (C) Homing pigeons trajectories under different conditions

Reference:

Lisowski C, Quetting M, Klaus D, Lazarevski L, Seep L, Germer M, Li J, Müller I, Zuniga D, Fiedler W, Dechmann DKN, Thorup K, Hasenauer J, Fester L, Kuerten S, Farle M, Wiedwald U, Wikelski M, Kurts C. Homing pigeon navigation relies on superparamagnetic macrophages under overcast conditions. Science. 2026 May 28;392(6801):985-991. doi: 10.1126/science.ady2486.