Why very weak radio-frequency noise disrupts the bird magnetic compass
In plain words
Experiments report that weak radio noise, far weaker than Earth's magnetic field, makes migratory birds lose their compass sense. Radical-pair theory predicts such weak noise should only work if the electron spins stay correlated far longer than seems possible.
Precise statement
Night-migratory songbirds reportedly lose magnetic orientation under broadband radio-frequency noise (reported from about $2\,\mathrm{kHz}$ up to about $85\,\mathrm{MHz}$, absent at $140\text{-}150\,\mathrm{MHz}$) with magnetic amplitudes in the nanotesla range, about $10^{-5}\text{ to }10^{-4}\,\mathrm{G}$. For a radical pair, a yield change of order 1 percent from a resonant field B_rf requires $\left(\gamma_e B_{\mathrm{rf}} T_2\right)^2 \sim 0.01$ with $\gamma_e = 1.76e7\,\mathrm{s}^{-1}\,\mathrm{G}^{-1}$, giving $T_2$ of tens of microseconds or more at $B_{\mathrm{rf}} \sim 1e-4\,\mathrm{G}$ (heuristic estimate), far above computed relaxation times. An answer is a mechanism that reproduces the amplitude and frequency thresholds of the effect, within or outside the radical-pair picture, or a demonstration that the effect is not reproducible.
What would settle it
Independent, blinded replications mapping the disorientation threshold versus RF frequency and amplitude, compared with a spin model that predicts that threshold curve.
Status in the literature
Unverified note
A 2023 PNAS study found no disruption above about 140 MHz, consistent with a predicted flavin radical-pair cutoff near 116 MHz; a 2026 J. R. Soc. Interface study found amplitude-modulated MHz fields disorient birds at lower amplitude than unmodulated ones and argued for a separate induction-based sensor.