The ability to perceive Earth’s magnetic field, which at one time was dismissed as a physical impossibility, is now known to exist in many animals. Laboratory tests show that animals as diverse as the European robin, the loggerhead sea turtle, the brown bat, the Caribbean spiny lobster and the red-spotted newt have magnetic compasses. How do they work? How do birds navigate between nesting areas separated by thousands of miles with pinpoint accuracy? Different theories have emerged from thousands of experiments…
My favourite author Borges wrote: A king goes to the kingdom of another king. The host puts him in a maze and it takes him many days to find his way out. But he says nothing, though seething inside, and issues an invitation for his host to visit him. When his host returns the visit, this king takes him to the middle of a desert and leaves him there saying that the previous maze was manmade. Now he needs to find his way out of God’s maze. As someone who has absolutely no sense of direction, I envy the abilities of animals to find their way through the alien landscape of the earth.
How do the Siberian birds get here year after year when the landscape below them changes so rapidly? How do the Monarch butterflies find their way from North to South Africa and to the exact place, often made unrecognisable by woodcutters? The Earth has a magnetic field. Every child who has been taught how to use a compass knows that. The ability to perceive Earth’s magnetic field, which at one time was dismissed as a physical impossibility, is now known to exist in many animals. Laboratory tests show that animals as diverse as the European robin, the loggerhead sea turtle, the brown bat, the Caribbean spiny lobster and the red-spotted newt have magnetic compasses. How do they work? How do birds navigate between nesting areas separated by thousands of miles with pinpoint accuracy? Different theories have emerged from thousands of experiments. Some experiments show that some animals navigate by “seeing” Earth’s magnetic field.
A study from the University of Oxford says that sunlight absorbed by molecules called Cryptochromes in the eyes of animals such as birds and bats triggers a chemical reaction making the molecules sensitive to the local magnetic field. This is known as chemical magnetoreception. Some scientists believe a second theory: that a mineral called magnetite, an iron-rich crystal with magnetic properties, in their bodies helps animals orient themselves in Earth’s magnetic field. Animals have internal stores of the mineral magnetite, which acts like little magnetic needles in the animals’ cells. Scientists believe the mineral may explain the strong directional sense found in aquatic migrants such as whales, sharks, tuna, trout, and sea turtles. Homing pigeons can locate their roosts from several thousand miles away. Because of this ability, people have used the birds to carry messages since the days of ancient Egypt.
According to biologists at the University of North Carolina magnetite is found inside the homing pigeons’ beaks. There is evidence to suggest that some birds may detect Earth’s magnetic field with receptors associated with their sense of smell. Are the cues visual or magnetic? Over the years laboratory experiments have shown that birds orient themselves based on cues from the sun, stars, Earth’s magnetic field, and by memorising landmarks while migrating. Biologists atPrinceton University teamed up with wildlife biologists of the Illinois Natural History Survey and University of Oldenburg in Germany to research on songbird navigation. They captured songbirds during their natural northward migration, exposed them to an altered magnetic field at sunset, and then tracked them for several nights. The night the birds were exposed at sunset to the altered magnetic field, which was pointed east (instead of magnetic north), they flew in the wrong direction—to the west.
The next night the songbirds flew off in the right direction—northward. This led the researchers to conclude that the thrushes used cues from the setting sun to update their internal magnetic compass and get back on the right track. The experiments suggest that the songbirds’ magnetic compass is calibrated on a daily basis, by visual cues.
How do crocodiles do it? Captured and relocated saltwater crocodiles swim hundreds of miles to return to their home rivers. A team of crocodile researchers took three crocodiles near bays in Queensland, Australia, and flew them by helicopter to coastal spots 52 and 130 kilometres away. Researchers kept tabs on the reptiles with a transmitter attached to the back of their heads. The data revealed that once in ocean waters, the animals covered 10-30 kilometres each day to reach home. One crocodile was transported 400 kilometres away. He took 20 days to reach home. No one knows how. Caribbean spiny lobsters are among the animal kingdom’s top navigators, able to determine their location on Earth even when transported to an unfamiliar area. To test the lobsters’ navigation abilities, researchers used measures to disorient and confuse the animals. Lobsters were displaced 12 to 37 kilometres from their point of capture. Divers gathered the lobsters and placed them in containers with seawater.
The containers were covered and transported to testing sites via circuitous routes by truck and boat. Further disorienting tricks were employed, such as suspending the containers by ropes so that they swung erratically, and lining them with magnets strong enough to alter the directional functions of compasses. Once at the test site, the lobsters, even with their eyes covered, invariably determined the direction of their capture site and began moving homeward. Hammerhead sharks gather in large groups around underwater mountains, or seamounts, during the day. They leave the area at night and spread out through the ocean for miles to feed, returning to the seamount every morning. They find their way through magnetic fields, made possible by the presence of electro-receptors at the bottom of their uniquely shaped heads. Seamounts, made of basalt, create magnetic bands of varying intensity. Loggerhead turtles are less than two inches long when they emerge from underground nests on the coasts.
They crawl straight from their shells and plunge into the waters and follow a circular route that goes round the Atlantic and back toward their birthplace on the same shore. The entire journey of 8,000 miles made by solitary defenceless sea turtles is done without any companions or parental education and takes five to ten years to complete. Scientists say they are born with a specific magnetic map. Blind mole rats live most of their lives underground in pitch-black, complex tunnel systems. They have to dig over great distances when foraging for bulbs and roots, and then have to find their way home again. Research done by the Tel Aviv University in Israel reveals that blind mole rats use the Earth’s magnetic field to continuously monitor and maintain their course and use it to correct errors as they travel. Blind mole rats have additional radar-like abilities to detect obstacles before they come into contact with them. Scientists found that when they blocked wild mole rats’ tunnels, the animals carefully dug out the shortest route around the obstacles to reconnect them. Furthermore, they left a safe margin of 10 to 20 centimetres around the obstacle. How amazing animals are. Instead of destroying them we should learn from them.