sweet homing: the tricks of animal navigation
you're exploring a cave with a group of people: the leader, in front,
is the only one with a light. She's up ahead, forging her way forward,
the light of her lamp lost around a distant corner. Around you,
the world is pitch black, but through the darkness you hear calls
of "over here!" and "follow me this way!" The
people in your group can navigate their way through the dark by
using sound to tell each other where they are and where they're
signal each other the same way as they move through the thousands
of miles of their migration path along the Pacific coast. Using
their whale songs as sonar, they can discern
the location of nearby members of their group, or pod. Some whale
researchers and activists worry that the Navy's use of low-frequency
active (LFA) sonar could interfere with whales' migration abilities,
separating some whales from the pod or causing others to strand
on the shore. There is already evidence to suggest that sonar, and
ocean noise pollution in general, is threatening many species of
Navy argues that for the most part, its short-term tests have shown
that whales usually return to their normal navigation after the
sonar sounds stop. And government officials have stressed the importance
of underwater surveillance in the wake of the Septermber 11th attacks.
For more on this debate, listen to Rebecca Roberts's story.
whales have magnetic material in their brains that may help
year, whales migrate from Hawaii to the northern Pacific coast,
and back. How do they manage to find the tiny islands in that vast
sea? Sonar may help them stay together and follow one another, but
they must use some other means to remember and relocate their destination.
researchers believe whales use biomagnetism to do this. We already
know about lots of animals and birds that use magnetic material
in their bodies to help them understand where they are. For example,
the Arctic tern makes a pilgrimmage from the North Pole to the South
Pole and back every year. The tern has a compound called biomagnetite
in its brain, that may make its brain cells sensitive to changes
in the earth's magentic field. As the tern flies, it may be able
to sense the direction of the surrounding magnetic field and use
that information to guide it.
has been found in the brains of whales and dolphins, and it is widely
believed that marine mammals use magnetism as well as sonar to direct
themselves during migration.
terns, like many other animals, use a combination of methods
to find their way during migration.
than any other sense, humans use their vision to navigate. We often
look for landmarks, and use them to tell us what direction we've
come from and to help us locate a path or nearby places. In other
words, we use what we see in combination with what we remember to
help us find our way home.
researchers believe whales and other animals do the same sort of
thing. The water whales migrate in is often too dark for them to
actually see features on the ocean floor. But just as sonar helps
them find food nearby, whales can also use their sounds to "see"
what's around them. They may remember a path defined by some landmarks
below them, and this may help them find their way along the coast
from Hawaii to Alaska.
animals who travel in brighter environments use their vision to
navigate. The arctic tern mentioned earlier also uses landmarks
like the African and European coastlines to help navigate its long
flight from pole to pole. During the night, stars and the moon can
guide the birds. Some insects, like locusts, also use the sun to
migrate. Even the sense of smell can lead animals home: scientists
believe the salmon's famous swim upstream to its birthplace is guided
by a signature smell of the fish's stream.