Global Positioning System Reference
In-Depth Information
physics, so perhaps we should expect that they will come up with similar
solutions.) So I conclude my account of the history of human navigation by
looking at examples of matching navigational techniques in the animal
world. Odd, I know, but revealing and somewhat humbling.
1
Piloting.
Recall the Phoenicians and Carthaginians, boldly going where
nobody had gone before (except for the residents of the African coasts that
they skirted) in their wooden sailing ships. The pilot of such a ship could
easily retrace his steps. That is to say, he could follow familiar landmarks to
his home. Doing this requires a map (perhaps physical or perhaps merely a
mental map) on which each landmark has its place relative to the home
port and from which the pilot can guide his ship home.
There are 130 species of digger wasps in existence; the females of some
species use piloting to find their way back to their nests. The nest entrances
are not visible from far away, so a wasp memorizes the local topography
and uses the mental map it has formed as a guide. We know this because, in
an experiment that is well known to zoologists, researchers moved some
prominent landmark features (such as pebbles) that were near one nest
site while the wasps were elsewhere. The returning wasps had di≈culty
finding the nest entrance and took much more time to do so than they had
needed before the landmarks were moved.
Compass.
Piloting requires a map but not a compass. Humans have devel-
oped a magnetic compass to indicate direction and have learned how to
navigate with this tool. So have birds. The main di√erence is that the birds'
compass is built-in. In fact, there are many di√erent compasses within the
animal world. One popular type (in the sense that many species have
evolved it) is based upon sensitivity to the geomagnetic field. Some birds
have small particles of natural magnetic material in their brains that pro-
vide them with a sense of direction, defining their orientation with respect
to the geomagnetic field. For example, consider the European cuckoo. As
soon as it has learned to fly, a young cuckoo migrates from its nest in, say,
western Scotland to wintering grounds in central Africa. It flies alone;
given the nature of cuckoos, we can hardly expect its parents to show it the
way. These young birds fly for thousands of miles over regions that they
have not visited before, and yet they all end up in the same broad area that
1. For more on the fascinating subject of animal navigation, see Denny and McFadzean
(2011). For animal remote sensing, see Denny (2007, chap. 5).
