Study links pigeon navigation to iron-rich liver cells; experts express skepticism
6 verified4 unconfirmed
A new study published in the journal Science proposes that homing pigeons navigate using iron-rich immune cells in their livers, which may act like a magnetic compass. Researchers found that pigeons whose liver macrophages were depleted with a drug lost their ability to navigate on overcast days but could still find their way on sunny days when visual cues were available. The study builds on previous clues that the liver and spleen have magnetic properties due to iron storage from red blood cell breakdown. The team used techniques such as vibrating sample magnetometry and magnetic cell separation on liver, spleen, and other tissues, identifying the strongest magnetic response in the liver. However, the paper does not fully explain how the cells detect Earth’s relatively weak magnetic field or transmit that information to the brain. Several outside experts remain skeptical, citing past studies that concluded similar iron-containing cells in beaks do not respond to geomagnetic fields. Critics also point to the lack of causal evidence and possible alternative explanations, such as the drug itself affecting the birds’ behavior. Despite the uncertainty, the hypothesis opens up new directions for research across different animal species.
What’s verified
The study was published in the journal Science.
Homing pigeons have iron-rich immune cells (macrophages) in their livers that may be involved in magnetic navigation.
Injecting pigeons with clodronate liposomes to deplete these macrophages disrupted their navigation on overcast days.
On sunny days, the macrophage-depleted pigeons could still navigate using solar cues.
The precise mechanism by which the liver cells might sense magnetic fields remains unknown.
The study has drawn skepticism from experts who note that similar earlier claims about magnetite in beaks were later refuted.
Not yet confirmed
One source mentions three primary hypotheses for avian magnetoreception: a compass mechanism using magnetic particles in the upper beak, biological ion channels sensitive to voltage, and retinal pigment effects enabled by light. The other source does not detail these hypotheses.
One source references a 2012 Nature study that refuted earlier claims of compasslike neurons in pigeon beaks, showing instead that the iron-bearing cells there were macrophages. This study’s implications are not discussed in the other source.
It is unclear whether the superparamagnetic properties of the macrophages are sufficient to respond to Earth’s magnetic field and notify neurons.
Questions remain about how the magnetic signal from the liver cells would be transmitted to the brain, as no pathway has been established.
Key figures
Clivia Lisowski, University of Bonn and University Hospital Bonn (study co-author)
Martin Wikelski, Max Planck Institute of Animal Behavior (study co-senior author)
Christian Kurts, University Hospital Bonn (study co-senior author)
Joe Kirschvink, California Institute of Technology (geobiologist, not involved in the study)
Carl Meyer, Hawaii Institute of Marine Biology (biologist, not involved)
Pascal Malkemper (neuroscientist, not involved in the study)
Sources: Ars Technica, scientificamerican.com
