Fig. 7. Map of magnetic field inclination along the southeastern coast of the United States. The isolines represent isoclinics (lines of equal magnetic field inclination). In this part of the world the isoclinics trend east–west, while the coastline is aligned approximately north–south. As a result, each area of coastline along the eastern seaboard is marked by a unique inclination angle. A similar pattern exists for the isolines of total intensity. A sea turtle navigating along the east coast to a particular coastal feeding or nesting area might thus hypothetically do so by detecting a single magnetic element such as inclination or intensity (see text for details).