Page 58 - The Miracle of Migration in Animals

THE MIRACLE OF MIGRATION IN ANIMALS

Advantages of Flying with Fat
Reserves

Before migrating, as already pointed out, birds consume as
much food as possible and convert these reserves into fat, which is
the most ideal fuel. Metabolizing one gram of fat releases twice as
much energy as the same quantity of protein and carbohydrate. In the
course of migration, birds use up this accumulated fat, but the weight
of fuel they carry presents certain difficulties. For example, the red-
necked stint carries a burden of fat exceeding 90% of its normal body
weight. The bird burns up this fat gradually on its non-stop migra-
tion journey.
To be able to carry
this excess load to a
given altitude, a bird
burns up a significant
amount of fuel. When it
reaches the necessary
altitude, the bird’s most
efficient method is to
continue its journey
Red-necked stint
without stopping until all
its fat reserve is used up. If it lands before using this supportive en-
ergy, it may encounter serious risks. For example, it may come down
some place where it can’t refuel quickly enough to continue. For this
reason, it is always more advantageous to store reserve energy to
complete the flight. 15
Every year, migrating shorebirds set off on a flight of 12,000 kilo-
meters (7,450 miles). Over the course of their lives, the total distance
they cover on these journeys is equivalent to the distance to the Moon
and back.

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