Signals too small to sense: physical and information-theoretic limits to induction-based magnetoreception in birds.

A recent study (Nordmann et al. 2025 Science 391, 1155-1160 (doi:10.1126/science.aea6425)) proposes that magnetoreception in pigeons may arise from electromagnetic induction within the semicircular canals of the inner ear. In this framework, motion through the geomagnetic field is suggested to generate an induced electromotive force that leads to ion redistribution in the endolymph, activation of voltage-gated calcium channels and subsequent engagement of downstream neural circuits. In this work, I examine the physical plausibility of this mechanism using a toy model of the induction process combined with an information-theoretic analysis. I find that, under idealized assumptions, Faraday induction in the semicircular canals would not generate a signal of sufficient informational content to support the extraction of directional magnetic field information from the geomagnetic field. However, the model supports the possibility of inferences due to radio-frequency electromagnetic waves of a miniscule amplitude, thereby providing a potential rationalization of their disruptive effect on avian compass navigation.