Fig. 8. A possible strategy for locating a specific target area using a single magnetic element such as inclination or intensity, illustrated here with an example of a sea turtle using the strategy to approach an oceanic island. The turtle needs to `know' the value of one magnetic element at the target and might also need some minimal information about the pattern of isolines in the region. Instead of attempting to steer directly toward the island, the animal swims on a path that is deliberately offset from the target by enough that the turtle will arrive at the appropriate magnetic isoline on a known side of the target. In this example, the turtle adopts a course that takes it well west of the island. Thus, when it arrives at the appropriate isoline, it knows to turn right and swim along the isoline toward the southeast rather than turning left and following the isoline northwest. Because the isoline intersects the target, the turtle locates the goal.