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Have an internal clock
The sand hoppers daily routine is governed
by its internal clock. This has been studied by taking a sand hopper into
a room with light 24 hours a day and any references to night or day were
missing. It was observed over a period of time that it still hid itself
at dawn and later showed itself at sunset.
Find their way home
The sand hoppers living area is very narrow.
They cannot live in or on the water, and the seaweed and sand cannot be
too wet or dry. If for example a sand hopper is blown off the beach by
the wind, it is able to find its way back to the beach. With the help
of its internal clock the sand hopper knows what times it is, and thereafter
uses the position of the sun or moon to orientate itself. The sand hopper
even has this ability on cloudy days and nights because it can see polarized
light.
Easily fooled
When sand hoppers were studied in a bay,
all the sand hoppers knew the direction to the sea. Sand hoppers on the
bays northern side moved south if they were moved too far up the beach,
while sand hoppers on the southern side moved north when they were moved
up the beach. But what happened when sand hoppers were moved from the
bays northern side to its south? They travelled in the wrong direction,
further away from the sea! They had used the same calculation of the sun
or moons angle as before.
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