Page 66 - The Miracle of Migration in Animals

THE MIRACLE OF MIGRATION IN ANIMALS

thought to be one and the same thing, and this assumption per-
sisted for a long time. After many years, the difference was ac-
knowledged. Only in the nineteenth century did it become
possible for ships to follow orthodrome rather than loxodrome-
based routes .19
To the astonishment of scientists, however, when black-
winged stilts migrate, they do not follow the loxodrome route that
one using a compass would normally expect. They follow an or-
thodromic route, which is shorter and more efficient—but very

difficult to determine, since it is possible to trace the shortest dis-
tance between two points on a spherical shape only when the
whole of the sphere is visible. For example, while it is simple
enough for us to join two points on the surface of an orange, we
can’t possibly know the shortest route from where we are
presently to Sydney, Australia. Similarly, however high up a bird
may fly at point A, it cannot visually determine the shortest route

to point C, thousands of kilometers away.
But birds are more successful than a pilot equipped with a
compass at finding the shortest (i.e. orthodrome) route to place
where they have never been. According to researchers, birds
achieve this thanks to a "sun compass." At every meridian they
o
pass when flying east, birds have to adjust their route by a 1 angle
of deviation. It is estimated that birds use the Sun’s constantly
changing position in the sky. Thanks to this complex navigational
ability, they can reduce traveling risks and the amount of energy

they use to a minimum. Finding the shortest route, as birds have
been shown to do by using the Sun, is something we humans can
do only after solving complex equations:

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