gnetic field. We might even speculate that systemic variations, or topographical peculiarities of the magnetic field might serve the pigeons as a grid or even as landmarks by which they are able to navigate (Kiepenheuer). In this context, vector navigation faces fewer difficulties. In order to gain magnetic compass information, a pigeon would have to measure the direction of the earth’s field with far less precision than if it were using this directly as a position-fixing cue. Changes in declination would result in navigational errors, but considering compass information alone the changes are relatively small (Lincoln 102). In the Northeastern United States, declination changes one degree in about 80 kilometers and in the regional anomalies mapped by variations of more than five degrees are infrequent. At geographically small, high-amplitude anomalies, the deviation of a magnetic compass can be larger (102). In conclusion, the interpretations of the observed magnetic effects on animal orientation seem paradoxical. Theories that might explain the animal’s extreme sensitivity appear to be ruled out by the earth’s field. Vector navigation, on the other hand, restricts the use of the earth’s magnetic field to compass information only, but this theory does not readily explain either the animal’s sensitivity to magnetic fields or sight-specific magnetic effects (Carthy 86). ...
