Scientists have recently unraveled the decades-old mystery of the pigeons travelling hundreds of miles. In a surprising research by the team at Max Planck Institute of Animal Behavior, it was found that pigeons possessed a unique navigation system. This goes deep into the microscopic cells in their bodies that may act like tiny magnetic sensors. These are iron-filled immune cells present in their livers. Birds lacking these cells struggled to find their way home under overcast skies, indicating they rely on Earth’s magnetic field for guidance. A study published in Science tells that pigeons have an internal navigation system in the liver consisting of specialized immune cells helping them to detect the magnetic field of the Earth.
WHAT ARE THESE CELLS?
Researchers found that these cells, called macrophages, accumulate iron while breaking down old red blood cells. The iron, being a magnetic substance, gives the cells unique magnetic properties that allow the birds to detect the earth’s magnetic field. They experimented by extracting the cells and observed that the pigeons were unable to find their way home. “We didn’t expect immune cells to act like sensors for magnetic fields at all. Our results reveal a previously unknown mechanism for magnetic perception in animals,” says Prof. Christian Kurts, Director at the Institute of Molecular Medicine and Experimental Immunology at the University Hospital Bonn, and one of the study’s co-senior authors. Prof. Martin Wikelski, Director at the Max Planck Institute of Animal Behavior and the other co-senior author of the study, further added that the perceived ‘gut feeling’ may actually have a physical basis.
THE PERSISTENT QUEST FOR BIRDSÊ MAGNETIC SENSE
Though the scientists have known that homing pigeons and migratory birds use Earth’s magnetic field as a navigation tool, the mystery of exactly how many birds possess this characteristic and detect their way still remains to be solved. Over the years, researchers have proposed various possibilities. Some theories suggested birds could dete ct magnetic f ields through light-sensitive molecules in their eyes. Others pointed to tiny magnetic particles in their beaks. The research team included scientists from the University of Bonn, the University Hospital Bonn, the University of Duisburg-Essen, and the Max Planck Institute of Animal Behavior (MPI-AB).
THE IRON-RICH LIVER CELLS
To determine the location of these cells and where magnetic sensing could occur, researchers of the team examined several multiple organs where magneto reception had occurred which included the eyes, the beak and the brain. They also analyzed the liver and spleen using techniques known as “vibrating sample magnetometry” and “magnetic cell separation.” “We had some clues that the liver and spleen have magnetic properties, because they break down red blood cells and so store much iron in the body,” says first author Dr. Clivia Lisowski, from the University of Bonn and the University Hospital Bonn, who led the immunological work. The results were striking. Among all the tissues studied, the liver contained the highest concentration of iron and produced the strongest magnetic response. “Iron is crystallized in oxide nanoparticles making the cells super paramagnetic and reactive to magnetic fields. We found by far the strongest magnetic response in liver tissue,” adds Prof. Ulf Wiedwald, from the University of Duisburg-Essen. Further investigation revealed that liver macrophages were responsible for the magnetic properties.
THE CRUCIAL ROLE OF THE EXPERIMENT
The researchers then tested whether the macrophages actually influence navigation. At the MPI-AB in Konstanz, Germany, pigeons had been trained to return to their aviary from locations more than twenty kilometers away. Scientists removed the liver macrophages and monitored how the birds performed. The results depended on the weather. On cloudy days, when the sun was not visible, the pigeons that lacked macrophages struggled to find their way back as they lost the sense of direction. Those with intact macrophages reached home in about 70 minutes. On sunny days, however, they successfully returned, likely relying on the sun as a navigational cue instead of Earth’s magnetic field.
THE TRAVEL TRACK OF THE MAGNETIC SENSE
It was now confirmed that there was a link between the liver cells and the navigation of the birds. The task was now to discover the magnetic signals which could reach to the brain as information. Using electron microscopy, they found that the iron-rich macrophages sit close to nerve fibers. This arrangement suggests a possible pathway through which magnetic information could be transmitted from the liver to the nervous system and ultimately to the brain. Lisowski says: “These findings provide the first concrete evidence of how the Earth’s magnetic field can be perceived within the body and passed on to the brain to guide movement.” “Animal navigation is one of the most fascinating phenomena in nature,” says Wikelski. “If immune cells are part of how birds sense reaction , it would fundamentally change how we understand navigation.”
DOES THIS EXTEND BEYOND BIRDS?
The study has answered many questions pertaining to the navigation systems in the birds. However, a question might arise- is this limited to just pigeons and some birds or goes beyond these waves? Animals such as sharks are known to navigate effectively without relying on light, raising the possibility that similar mechanisms could exist in other species. The researchers suggest that many animals, and perhaps even humans, may respond to magnetic fields in ways that are not yet fully understood.