Pigeons sense Earth’s magnetic field in an unexpected way

In experiments with 27 pigeons in Munich, Germany, researchers found that magnetic sensing originates in the inner ear, where movement generates minute electrical signals.

Brain mapping revealed that the signal travels from the balance centers to regions associated with navigation, offering fresh insight into how birds find their way.

Sensing Earth’s magnetic field

Scientists call it magnetoreception, sensing magnetic fields for direction and position, and it shows up across many animal groups.

For migratory birds, that extra cue can steer long flights when clouds hide stars and landmarks disappear.

Researchers still debate where the sensor sits, because magnetic information must become nerve signals before the brain can use it.

Two main theories

One review describes a radical pair, two linked electrons whose reactions depend on magnetism, inside light-sensitive cryptochromes in the eye.

Because those proteins respond to light, many lab studies test birds under dim illumination to check whether their compass flips.

Another theory points to magnetite, naturally magnetic iron oxide crystals, that could pull on nearby sensors and start nerve signals.

How do pigeons sense the magnetic field?

A 2012 study found iron-rich clusters in pigeon beaks were macrophages, immune cells that clean up old blood.

That result did not erase magnetite ideas entirely, but it warned scientists that iron deposits can fool careful anatomy work.

With the beak target less certain, attention returned to the inner ear, which already links sensation and movement.

The vestibular system is made up of inner-ear balance sensors that track head movement. The system relies on three fluid loops called semicircular canals.

When the head turns, that fluid pushes a gelatin cap, bending sensors and letting the brain measure rotation speed.

More than a century ago, scientists proposed that motion through Earth’s field could induce weak currents in that fluid.

Early brain clues

In 2012, a paper recorded single neurons in the pigeon brainstem tracking magnetic direction and strength.

Those neurons sat in vestibular nuclei, brainstem hubs that receive inner-ear signals, hinting that balance pathways might carry magnetic input.

The earlier recordings did not identify which cells start the signal, and they could not rule out other sensors elsewhere.

A 2019 study pointed to electromagnetic induction, electricity created when motion crosses a magnetic field, inside pigeon semicircular canals.

The researchers estimated that normal head bobbing could generate voltages large enough to affect sensitive channels on ear cells. That idea built a bridge from physics to biology, but it still needed a clear map of the brain circuit.

Lab experiment setup

The latest study was led by Dr. David A. Keays at Ludwig Maximilian University of Munich (LMU). The team used whole-brain activity mapping in Columba livia and then profiled ear cells one-by-one.

In a shielded room at LMU, they nulled background fields, then rotated a 150 microtesla signal for 72 minutes.

The researchers stained brains for c-FOS, a gene that flags neurons recently active, so magnetic sensing left a visible trail.

In darkness, the same brain regions still lit up, which argues against an eye-based magnetic sensor in the retina.

The brain signal path

The magnetic stimulus activated vestibular nuclei first, then reached the mesopallium, a brain area that blends many senses.

From there, signals also appeared in the hippocampus, a memory center for places and routes, which fits long-distance navigation.

The team saw little change across the rest of the brain, suggesting a targeted circuit rather than a global alarm.

Key ear cells

In the semicircular canals, hair cells – inner-ear sensors with bristles that trigger nerve signals – sit beneath a gel cap.

The team used single-cell RNA sequencing, reading which genes each individual cell uses, to compare hair-cell types.

One hair-cell class carried many voltage-gated ion channels, proteins that open when electrical charge changes, making it sensitive to induced currents.

Motion versus magnetism

Normal head rotation bends a cupula, a gelatin flap that bends during head turns, and that produces balance signals.

Induction adds a second input, because moving fluid through a magnetic field can push charged particles to opposite sides.

When the cupula stays still but charge shifts across it, the brain may tag that pattern as magnetic information.

Magnetic sensing without light

Unlike cryptochrome-based sensing, induction can work in complete darkness, because it depends on motion and conductivity, not photons.

That difference hints that birds may carry more than one magnetic tool, picking whichever matches the cues available.

The semicircular canals also respond during head scanning, so magnetic cues could be sampled while the bird checks its surroundings.

Limitations and skepticism

Neural activation cannot yet prove pigeons use this signal outdoors, because lab fields and natural cues might interact.

What happens if those channels are blocked in the ear, and do the birds still find home afterward?

Other species may solve magnetism with different hardware, so inner-ear induction might explain some navigators, not all.

Finding hidden magnetic sensors

Earth’s field varies in strength and tilt, and its inclination, the angle it dips into the ground, changes with latitude.

If the vestibular circuit reads that tilt, it could give a bird a built-in way to tell poleward from equatorward.

Field intensity might add a rough location cue, because the signal grows stronger in some regions and weaker in others.

The next challenge is connecting these signals to real homing decisions, from the first ear impulse to a turn in flight.

As teams test other birds and animals, the LMU results suggest the inner ear may hide more magnetic sensors.

The study is published in the journal Science.

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