Animal magnetism – Nature’s own satellite navigation system
The Earth produces its own magnetic field, which emanates from its magnetic inner iron core. On the Earth’s surface the magnetic field is extremely weak compared to the permanent magnets used in many every day appliances. At the magnetic poles the Earth’s magnetic field is approximately 0.7 Gauss compared to the Gauss value of a relatively small 10mm diameter x 5mm thick N42 neodymium magnet which can reach 5100 Gauss.
It is this magnetic field that makes a compass point north but for many species, the Earth’s magnetic field has a much more profound role…
Easily the smallest living organisms on our planet affected by the Earth’s magnetic field are what’s known as magnetotactic bacteria or to give them their catchy name, MTB. Discovered in 1975, these microscopic organisms that live in ponds and lakes with little oxygen have been found to align themselves along the Earth’s magnetic field lines. This is believed to happen because of the bacteria’s cellular composition and the existence of tiny magnetic domains within the bacteria. There is significant commercial interest in these tiny marvels with scientists researching the possibility of using them in magnetic recording equipment and magnetically targeted drug treatment.
Moving up the species scale are leafcutter ants; these critters prefer more tropical climates. They are known to travel far from their nests in search of leaves for their colonies and scientists believe that these ants have a ‘sixth sense’ that helps them navigate, an internal magnetic compass. To test this theory scientist have exposed the ants to powerful magnetic fields which disrupted the local magnetic field and threw the foraging ants off course. This sixth sense has been attributed to specks of magnetite (a magnetic mineral found in soil) in their antennae.
Bats are famous for using echolocation to perceive their surroundings by emitting ultrasonic sounds. A large proportion of bats also migrate hundreds of miles to hibernate each year and for this they rely on a different skill entirely, the ability to detect the polarity of the Earth’s magnetic field. This means they can detect whether they are flying north or south!
According to researchers, many species of birds use magnetic particles with their body to navigate using the Earth’s magnetic field. Slightly different to bats, birds are believed to perceive the inclination of the Earth to assess latitude. A species known as the Sooty Shearwater migrates nearly 40,000 miles every year!
Another great navigator is the salmon. After years feeding in the vast seas, salmon travel huge distances to familiar waters where they were hatched. This has baffled scientist for years, until recently when evidence was found that suggested that salmon use the Earth’s magnetic field to reach their spawning grounds by memorising the location’s magnetic field.
Like the salmon the loggerhead sea turtle is able to navigate thousands of miles of sea to return to the very beach where it hatched. The baby turtles spend just 24 hours on their hatching ground before dragging their tiny bodies into the sea and commencing a loop around the Atlantic Ocean before returning to nest. Like the salmon, scientists believe the turtles create a mental map that they use to determine both longitude and latitude. Researchers believe that the turtles create their mental map by combining information about the angle of the magnetic field with its intensity.
The humpback whale holds the record for the longest migration of any mammal on Earth. In 2011, a female humpback whale was tracked making a journey of over 6,000 miles from breeding areas in Brazil to those in Madagascar. Unlike many migratory species, the humpback whale continues to baffle scientists however. Scientists have analysed the migratory patterns of whales and they never veer more than a few degrees off their intended course despite travelling huge distances. An obvious possibility would be that they use the Earth’s magnetic field but the paths taken by different whales monitored are significant and the variation of the Earth’s magnetic field too great to discern any reliable correlation.
A grey area is that of ‘magnetoception’ in humans, this perceptive sense is still to be proven but tests showed that a protein found in the human eye, when placed in fruit flies gave them the ability to detect magnetic fields and use these to navigate towards or away from induced magnetic fields. Scientists are still trying to figure out how humans use this sixth sense, so ‘watch’ this space…