If you were lost in the middle of the woods and could not see the Sun, you might use a compass to try to decide which direction to take. A magnetic compass needle lines itself up with Earth’s magnetic field and points roughly north and south: from that, you can figure out east and west, too. Because this works fairly well, people have been using magnetic compasses to find their way for about 1,000 years.
But how do other animals find their way? How do birds navigate when it is cloudy? You probably know that many animals rely on their sense of smell to keep track of where they have been and where other animals are. However, some animals migrate (travel from one place to another), regularly covering hundreds or even thousands of kilometers each year.
It seems unlikely that animals could repeat such long trips accurately if they were relying only on their sense of smell, so scientists have been looking for evidence of what else animals may use to navigate. There are scientific investigations into whether animals use the Sun and Moon, Earth’s magnetic field, or recognition of landmarks to repeat their long journeys.
Homing pigeons are famous for being able to navigate extremely long distances. Their “homing” is so reliable that they were used in World War I and World War II to deliver messages over enemy lines. How do homing pigeons find their way— even on cloudy days? Do they carry a map and a compass?
What is Magnetoreception?
Magnetoreception is a sense which allows an organism to detect the Earth’s magnetic field. Animals with this sense include arthropods, molluscs, and vertebrates (fish, amphibians, reptiles, birds, and mammals, though not humans). The sense is mainly used for orientation and navigation, but it may help some animals to form regional maps. This effect is extremely sensitive to weak magnetic fields, and readily disturbed by radio-frequency interference, unlike a conventional iron compass.
In humans, deposits of magnetite have been found in bones in our noses.
How Do Birds Navigate?
Human-made compasses work by using Earth as an enormous magnet and orienting a tiny magnet attached to a needle to the planet’s north and south poles.
Scientists have thought for years that migratory birds may use an internal compass to navigate between their nesting areas and wintering grounds, which can be separated by thousands of miles.
Researchers have discovered a small spot on the beak of pigeons and some other birds that contains magnetite. Magnetite is a magnetized rock, which may act as a tiny GPS unit for the homing pigeon by giving it information about its position relative to Earth’s poles. Researchers have also found some specialized cells in birds’ eyes that may help them see magnetic fields.
It is thought that birds can use both the beak magnetite and the eye sensors to travel long distances over areas that do not have many landmarks, such as the ocean.
Experiments on migratory birds suggest that they make use of a cryptochrome protein in the eye, relying on the quantum radical pair mechanism to perceive magnetic fields.
Do Other Animals Have Magnetic Sense?
A variety of species—bacteria, snails, frogs, lobsters—seem to detect Earth’s magnetic field, alongwith migratory birds which rely on it for navigation.
Cartilaginous fish including sharks and stingrays can detect small variations in electric potential with their electroreceptive organs, the ampullae of Lorenzini. These appear to be able to detect magnetic fields by induction. There is some evidence that these fish use magnetic fields in navigation.