Bar magnets mask the effect of normal magnetic disturbances on pigeon orientation

Summary

In a previous publication we reported a correlation between normal fluctuations of the earth's magnetic field and the day-to-day variations in the initial bearings chosen by homing pigeons released repeatedly at a single test site under sunny skies. We here examine the question whether this correlation reflects a cause-and-effect relationship. A series of 20 test releases was conducted in 1974 to compare the bearings of pigeons wearing bar magnets glued to their backs with the bearings of pigeons wearing brass bars. As in a pilot series conducted in 1970, the day-to-day variations in the bearings of the birds wearing brasses were inversely correlated with the variations in the K index of magnetic disturbance, whereas no such correlation was found for the bearings of the birds wearing magnets. We conclude that the magnets mask the effect of the K fluctuations, which suggests that it is the magnetic events themselves that influence the orientational response of normal pigeons. This conclusion is further supported by a demonstration that bar magnets, like natural magnetic disturbances, deflect the birds' bearings to the left.