  It is known that more than 50 species use the Earth's magnetic field for
orientation and navigation. Intensive studies particularly behavior experiments
with birds, provide support for a chemical compass based on magnetically
sensitive free radical reactions as a source of this sense. However, the
fundamental question of how quantum coherence plays an essential role in such a
chemical compass model of avian magnetoreception yet remains controversial.
Here, we show that the essence of the chemical compass model can be understood
in analogy to a quantum interferometer exploiting global quantum coherence
rather than any subsystem coherence. Within the framework of quantum metrology,
we quantify global quantum coherence and correlate it with the function of
chemical magnetoreception. Our results allow us to understand and predict how
various factors can affect the performance of a chemical compass from the
unique perspective of quantum coherence assisted metrology. This represents a
crucial step to affirm a direct connection between quantum coherence and the
function of a chemical compass.
