Pigeon's Natural Compass Found in Heart, Not Beak or Eyes
How homing pigeons navigate hundreds of kilometres and still find their way home has baffled scientists for decades. A recent study published in the journal Science has now revealed a surprising answer: the internal navigation system is located in the heart.
Researchers discovered that pigeons use specialised immune cells in their liver called macrophages. These cells collect iron while breaking down old red blood cells. The iron content gives the macrophages unique magnetic properties, allowing them to respond to Earth’s magnetic field and function as a natural compass.
‘We never suspected immune cells could act as sensors for magnetic fields. Our research uncovered a previously unknown mechanism for animal magnetoreception,’ said Professor Christian Kurts, Director of the Institute of Experimental Immunology and Molecular Medicine at Bonn University Hospital, one of the lead authors of the study.
‘What appears to be a ’gut feeling’ in bird navigation may actually have a physical basis,’ added Professor Martin Wikelski, Director of the Max Planck Institute for Animal Behaviour and another lead author.
To test the theory, a joint team of German universities tested trained homing pigeons released from over 20 kilometres away. Scientists removed the liver macrophages and monitored their flying ability.
The results depended heavily on weather. On cloudy days when the sun was hidden, pigeons without liver macrophages became disoriented and struggled to return home. Conversely, on sunny days, they successfully navigated back by relying on the sun rather than Earth’s magnetic field.
The research also revealed how magnetic signals are transmitted to the brain. Using electron microscopy, scientists detected that iron-rich macrophages are positioned very close to nerve fibres. This proximity provides a potential pathway for magnetic information to be transmitted from the liver to the central nervous system.
‘This finding provides the first concrete evidence of how Earth’s magnetic field can be sensed within the body and relayed to the brain to guide movement,’ said Dr Clivia Lisowski, the study’s first author from Bonn University.
The remarkable discovery unites various known biological processes, from iron metabolism to communication between the immune and nervous systems.
‘Animal navigation is one of nature’s most fascinating phenomena,’ said Wikelski. ‘If immune cells are part of how birds sense direction, it will fundamentally change how we understand navigation.’
Researchers added that this discovery opens the possibility of similar mechanisms in other species. Sharks, known for effective navigation without relying on light, are suspected to have a similar sensory system. There is even a possibility humans may respond to magnetic fields in ways not yet fully understood.