Pigeons Navigate Using Magnetic Sensors Hidden in Their Livers, Study Finds

A Mystery Decades in the Making

For a long time scientists have known that birds can somehow feel the pull of Earth's magnetic field and use it to find their way across vast distances. What they could not pin down was the actual biological hardware doing the sensing. A study published this week in the journal Science has finally located an answer in one of the least expected places: the pigeon's liver.

An Unlikely Organ

Researchers screened the eyes, beaks, brains, spleens, and livers of homing pigeons, and the liver stood out with the highest concentration of iron and the strongest magnetic response. The cells responsible are macrophages, immune cells whose normal job is to break down old red blood cells. In doing so they hoard iron, which crystallises into oxide nanoparticles. This makes the cells superparamagnetic, meaning they can align with and respond to an external magnetic field.

"When pigeons fly, the nanoparticles align with the magnetic field and become magnetised," said Clivia Lisowski, a co-author and postdoctoral immunology researcher at the University of Bonn. "Like that, pigeons can sense Earth's magnetic field."

From Liver to Brain

Electron microscopy showed these iron-laden macrophages sitting close to nerve fibres in the liver, hinting at a route for magnetic information to travel up to the brain. The behavioural evidence was striking. The team trained pigeons to fly home from over twenty kilometres away to an aviary at the Max Planck Institute of Animal Behavior in Konstanz, Germany. When the macrophages were temporarily removed and the birds released, they "just couldn't find their way," said Christian Kurts of the University of Bonn.

Crucially, the navigation failure happened only on overcast days. When the sun was visible, the pigeons still made it home using solar cues, showing the birds rely on both visual and magnetic systems working together.

Solving a Long-Standing Puzzle

"These findings provide the first concrete evidence of how Earth's magnetic field can be perceived within the body and passed on to the brain to guide movement," Lisowski said. The work overturns earlier hypotheses that placed the magnetic sensor in the beak or eyes, and it opens fresh questions about whether other migratory animals carry a similar hidden compass inside them.