Noise-Assisted Response Shelves and Angular Drift in Radical Pair Magnetoreception

We report that magnetic-field sensitivity in radical pair magnetoreception self-organizes into discrete, robust response shelves rather than scaling monotonically with microscopic parameters. Across extensive numerical scans of recombination asymmetry, hyperfine coupling, exchange interaction, and environmental dephasing, we identify a single shelf—within the explored class of RPM-like open quantum systems—centered at kS/kT ≈ 8–10 (u* ≈ 0.9 in log10 units) that persists across four decades of parameter variation. When centered and normalized, all response curves collapse onto a common functional form with pairwise correlations ≥0.99, demonstrating ratio-controlled timescale locking. The shelf peak position is invariant under hyperfine rescaling, while its amplitude scales as ΔYmax ∝ A^1.40 (R² = 0.989), indicating nonlinear interplay between coherent spin mixing and dissipative recombination. Hyperfine ablation (A → 0) confirms the shelf is proton-driven. At high magnetic fields (B ≳ 1 mT), we observe a hyperfine-controlled angular drift revealing a Zeeman–hyperfine interference transition. This work does not propose new quantum mechanisms, but identifies a general organizational principle governing how known quantum dynamics are converted into robust biological function within the explored model class. Because the present analysis employs a minimal single-nucleus radical pair, generalization to multi-nuclear cryptochrome geometries remains to be established. These findings establish response shelves as a general organizing principle for noisy quantum sensors in this model class and provide testable predictions for cryptochrome-based magnetoreception.