The radical pair mechanism can provide a sensitive and robust magnetic compass for birds.

Many adult birds can travel 5,000km or more with a precision of centimeters. Earth's magnetic field provides an omnipresent source of information that aides in this navigation. The mechanism by which animals sense the Earth's magnetic field remains one of the most important problems in sensory biology. The radical pair mechanism (RPM) proposes that the Earth's magnetic field influences a chemical pathway via electron spins in a radical pair. Recently it has been shown that a so called “quantum needle” radical pair model can be extraordinarily sensitive to directional changes, thus potentially providing the basis for a highly sensitive magnetic. However, it has also been shown that many compass systems are fragile, i.e. that even small, naturally occurring, variations in parameters can abolish effects that are observed in models without considering such noise. Here, we ask what effects noise has on a quantum needle compass system. Rather than reducing the quantum needle, noise is found to either leave the needle intact or even enhance it in some systems. This suggest that a quantum needle based compass may not only be distinguished by a high sensitivity, but also by being unusually robust to noise, making it a highly optimized system for magnetoreception.