Page 100 - The Miracle of Migration in Animals

THE MIRACLE OF MIGRATION IN ANIMALS

The Orientation Skills of Bats

Bats are nocturnal mammals, of which there are as many as
900 different species. They spend the winter in caves or mines,
since these places supply a humid atmosphere that never falls
below freezing, factors necessary for hibernation, where bats can
pass the winter in a torpid state.
When they awaken from hibernation, their seasonal migra-
tions begin. To find food, bats travel many kilometers. Some species
of bat weigh less than 20 grams (3/4 ounce), yet despite their small
bodies, some can migrate 1,000 to 1,500 kilometers (620 to 930
miles). 30
Cave-dwelling bats have a problem to deal with. Their envi-
ronment of constant temperature and humidity prevents them
from knowing what the weather is like outside. However, they can
perceive changes in air pressure, thanks to a structure in their mid-
dle ear known as the vitali organ.
By monitoring barometric pressure, the eastern pipistrelle
bats of North America can sense when its prey, the moths, are fly-
ing and even at what altitude. The bat’s barometric sensor has an-
other function; at every moment, the bat knows exactly how high
from the ground it is. 31
It is not known exactly how bats navigate, but researchers be-
lieve that they use sight, as well as hearing and smell. Yet these as-
sumptions do not completely explain the bats’ navigational
abilities. They travel at night and, as is well known, make use of
echolocation during flight. Their vision isn’t sufficiently developed
for them to determine direction, and their echolocation is only ef-
fective up to a certain distance. The signals they emit using the
tongue or larynx bounce back from objects and are perceived by the

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