Why animals respond to the full moon: Magnetic hypothesis

Abstract

The geomagnetic field is typically about 50 μT (range 20–90 μT). Geomagnetic activity generally decreases by about 4% for the seven days leading up to a full moon, and increases by about 4% after the full moon, lasting for seven days. Animals can clearly detect the changes in magnetic field intensity that occur at full moon, as it has been shown that variations of just a few tens of nT are adequate to form a useful magnetic ‘map’. We think that moonlight increases the sensitivity of animals' magnetoreception because the radical pair model predicts that magnetoreception is light dependent. In fact, there have been some reports of changes in the sensitivity of magnetoreception with lunar phase. We propose a hypothesis that animals respond to the full moon because of changes in geomagnetic fields, and that the sensitivity of animals' magnetoreception increases at this time.