Search for the compass needles

Abstract

The idea that bird orientation is guided by magnetic-sensing structures in the animals' beaks has been challenged by the suggestion that the iron-containing cells are macrophages, which have no link to the brain. See Letter p.367 How do migratory birds detect magnetic fields? Previous studies described a magnetic sensing system consisting of magnetite-containing dendrites in the upper beak, which were thought to support the animals' ability to navigate using magnetic fields. That widely accepted model is now brought into question. Through a comprehensive anatomical characterization, David Keays and colleagues show that the iron-rich cells in the beak of the pigeon Columbia livia are in fact macrophages, not magnetosensitive neurons. Iron-rich macrophages are not unique to the bird's beak. Thus the neural basis of magnetoreception in birds remains elusive; a candidate site for this property is the olfactory epithelium, a sensory structure that has been implicated in magnetoreception in the rainbow trout.