An iron compass in the liver: superparamagnetic macrophages give homing pigeons a magnetic sense

In a recent study published in Science, Lisowski et al. identified superparamagnetic, iron-loaded macrophages in the pigeon liver and showed that depletion of clodronate-sensitive phagocytic cells impaired homing under overcast skies, when solar cues were unavailable. 1 Together, these observations point to a light-independent magnetoreceptive system outside the head and broaden current models of magnetoreception beyond receptors based on cryptochrome, magnetite, and ion channels in the eye and beak. 2