KentuckyFC writes "How birds use the Earth's magnetic field to navigate has puzzled researchers for decades. In recent years, a growing body of evidence has pointed to the possibility that a weak magnetic field can influence the outcome of a certain type of chemical reaction involving the recombination of pairs of ions in bird retinas. The trouble is that the ion recombination is known to happen too quickly for the Earth's weak magnetic field to have any effect. Now it looks as if the quantum Zeno effect explains all, says one researcher (abstract). This is the watched-pot-never-boils effect in which the act of observing a quantum system maintains it for longer than expected. That's extraordinary news because it means a quantum sensor is determining the macroscopic behavior of living birds."