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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.
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