Overview
- Researchers used lab magnetometry, electron microscopy and GPS-tracked homing trials to show that pigeon liver macrophages contain iron particles with superparamagnetic signatures and often lie next to nerve fibers.
- In behavioral tests, roughly half of 34 trained homing pigeons were given a macrophage-depleting drug and those birds failed to orient on a fully overcast day while untreated birds returned within about 70 minutes.
- Authors propose a mechanism where iron from broken red blood cells forms nanoparticles in hepatic macrophages that could respond to Earth’s field and signal the brain via nearby nerves, but the pathway has not been directly traced.
- Outside experts have flagged key caveats: the depletion drug acts systemically so effects cannot be pinned to the liver, lab magnets used in some assays were much stronger than Earth’s field, and superparamagnetic particles may not produce a usable signal at geomagnetic strengths.
- If confirmed by liver-specific manipulations, direct neural tracing and replication across labs and species, the finding would add a new immune‑sensory route to navigation without excluding other proposed systems such as eye cryptochromes or beak-based magnetite.