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

TL;DR

This work examines the physical plausibility of magnetoreception in pigeons using a toy model of the induction process combined with an information-theoretic analysis, indicating that a functionally competent magnetosensory system likely relies on different sensing principles or, if induction-based, on a different sensing architecture.

Abstract

A recent study [Science 2025, eaea6425] 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, we examine the physical plausibility of this mechanism using a toy model of the induction process combined with an information-theoretic analysis. We find that, under idealised 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 (RF) electromagnetic waves of a miniscule amplitude, thereby providing a potential rationalisation of their disruptive effect on avian compass navigation. We stress that our analysis does not call into question the experimental evidence for magnetically responsive pathways within the vestibular system of pigeons. Rather, it constrains the class of viable physical mechanisms, indicating that a functionally competent magnetosensory system likely relies on different sensing principles or, if induction-based, on a different sensing architecture, while highlighting induction as a potential interference pathway of RF electromagnetic fields.

Figures (3)

• Figure 1: Summary of the toy model of induction-based magnetoreception via a dielectric-gapped electrolyte ring.
• Figure 2: Charge distribution $\tilde{\rho}$, a), and induced potential difference over the electrolyte $\tilde{V}_{\ell}$, b) and c), of a harmonically driven dielectric-electrolyte ring. a) gives the normalized charge accumulation over the entire electrolyte and, as an insert, within the nanometre-sized boundary zone at the electrolyte-dielectric interface. b) and c) illustrate $\tilde{V}_{\ell}$ as a function of the width of the cupula width $G$, in b) for the idealised non-conducting cupula of variable relative dielectric constant $\varepsilon_{r,g}$ as indicated; and in c) for the conductive cupula of $\varepsilon_{r,g}=100$ with conductivity $\sigma_g$ as indicated. The red dashed line in c) uses the conductivity of isoelectric gelatin gel. The cupula is actually expected to have electrical conductivity essentially identical to that of the surrounding electrolyte, i.e. $\sigma_g\approx\sigma_0$. The details of the calculation and parameters used are specified in the text. The grey dashed lines indicate the total electromotive force.
• Figure 3: Induced potential difference across the electrolyte $\tilde{V}_{\ell}$ for the ring sensor driven by rf-electromagnetic fields. a) $\tilde{V}_{\ell}$ for a $1$MHz electromagnetic field of $50$nT amplitude as a function of the width of the cupula $G$, idealized to be non-conducting. b) $\tilde{V}_{\ell}$ for $G = 340 \mu$m as a function of the rf frequency, with other parameters as for a). Results are shown for two relative dielectric constants of the cupula, as indicated on the graphs. The grey dashed lines indicate the total electromotive force.