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From: Bonner N, 1993, "Whales of the World", Blandford, pp115/6:

Live strandings ... show a distribution that is related to an
important, but little known, geophysical pattern - the total
geomagnetic field of the Earth. Margaret Klinowska has shown that all
the British live strandings occur where geomagnetic contours cross the
coastline at right angles. She suggests that the whales use the total
geomagnetic field as a map, using not the directional differences (as
we do with a compass), but the small relative differences in total
field.

The total geomagnetic field fluctuates in a fairly regular manner each
day, and it is possible that whales use these fluctuations as a timer
to tell how long they have been travelling, coupled with a learnt or
instinctive tendency to follow a field of constant strength, that is,
to follow a geomagnetic contour. This ability might be the basis of a
system of whale navigation.

Klinowska noticed that live strandings tended to occur on days on
which the daily fluctuation had been obscured by solar activity or
other irregular changes. On the south coast of Britain, strandings
occurred two days after a magnetically disturbed morning, while on the
north coast it was about a day and a half later. Looking at the
geomagnetic map, she discovered that there were two major geomagnetic
crossroads near the United Kingdom, one about a day and a half's swim
from the Scottish coast, the other about two days from the south
coast. This suggested to Klinowska that the doomed whales made their
mistake while still some distance from land, but then swam on
regardless, following a contour till it lead them, not past the coast,
but straight onshore. This theory could account for the often observed
fact that beached whales, when towed back out to sea, swim to the
shore once more. They are, it seems, convinced that is the right
direction in which to travel.

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