A strong magnetic anomaly affects pigeon navigation.

Pigeons were released in a strong magnetic anomaly with fast changes in intensity and gradients directions, about 60 km from their loft, and, for comparison, at the border of the anomaly and at a control site. The vanishing bearings were found to be closely related to the home direction, but unrelated to the local gradient directions. The vector lengths and the vanishing intervals, however, were significantly correlated with the maximum difference in intensity within a 2.5 km radius around the release site. This correlation was negative for the vector lengths and positive for the vanishing intervals, indicating that steep local gradients increase scatter between pigeons and delay their departure. These findings suggest that an irregular, fast changing magnetic field as found in the anomaly leads to confusion during the navigational processes. This, in turn, implies that pigeons can sense the respective changes in magnetic intensity. Magnetic cues seem to be included in the normal navigational processes that determine the departure direction.