For decades, scientists have searched for the biological machinery that allows birds, fish, and turtles to orient themselves by Earth’s magnetic field — a phenomenon called magnetoreception that is widely observed but stubbornly elusive. The leading hypotheses have focused on the head: light-sensitive receptors in the retina, microscopic iron crystals in the beak, or magnetite-based structures in the inner ear. A study published Wednesday upends that geography, pointing instead to the liver.
The research, led by Simon Spiro of the University of Oxford and Hal Drakesmith of the University of Oxford and the University of Manchester, isolated macrophages — immune cells that normally engulf pathogens and debris — from the livers of homing pigeons. When the researchers placed those cells under a slowly rotating magnetic field, the macrophages physically spun in lockstep, rotating with the field as if they were tiny compass needles.
Chemical analysis revealed that the macrophages were loaded with non-heme iron, a form of the metal not bound to hemoglobin. The liver cells contained far more iron than macrophages taken from the spleen, where old blood cells are recycled.
The team then tested macrophages from other bird species — chickens, starlings, and robins — and found that they, too, spun in the magnetic field. Mammalian macrophages, by contrast, did not react, suggesting the trait may be a bird-specific adaptation.
Martin Wikelski, a biologist at the Max Planck Institute of Animal Behavior who was not involved in the study, said the finding marks a significant shift. “The magnetic sense has been this mystery for almost 100 years,” Wikelski said. “This opens a completely new direction.”
Pigeons have been bred as messengers for thousands of years, carrying news, military dispatches, and even financial data over hundreds of miles in a single day. The mystery of how they find their way has resisted generations of inquiry.
The authors caution that the liver cells are “not a proven navigational organ.” The mechanism by which a spinning cell would transmit directional information to the brain remains entirely unknown, and the study does not establish that the cells are actually used for navigation in living birds. But the discovery provides a new target for researchers who have spent a century guessing at the biology of the magnetic sense.