Nature’s Radars

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There are sounds that we, humans, cannot hear, perhaps because their frequency is too low or too high. Animals, however, are not like us; some hear sounds that we cannot. That is where echolocation comes in handy to animals.

Bats get much of the details they need to find food or to explore the environment around them through echolocation. They click, squeal, and scream, emitting sounds up to 120 decibels, and detecting the echoes produced by these sounds. These echoes give them a huge amount of information about their surroundings.

The time it takes for an echo to return, for example, reveals the distance of an object; the changes in the sound’s frequency as it bounces off another creature can even reveal the speed and direction of the animal’s movement. Special ear and brain adaptations enable them to use this ability very much like a radar; they have enlarged ear flaps that gather and direct sound towards thin and extremely sensitive eardrums.

On the other hand, the flow of molten material in the Earth’s core, and the flow of ions in the atmosphere generate a magnetic field that surrounds the Earth. This magnetic field is used by many animals to give them directions.

We have invented the compass to help us better navigate by detecting the Magnetic North; animals with the magnetic sense use it for direction and long distance travel. Many use it to locate their homes, while others use it when migrating from one place to another; it is basically their own compass, which they have been using way before humans invented it.

Scientists researching this amazing magnetic sense in animals have found that animals with this sense have deposits of magnetite—an iron-rich magnetic material—in their nervous system. Even though scientists do not yet know how these structures work, some suspect that they excite membranes inside neurons and trigger nerve impulses that send direction-related information to the brain. They basically act like microscopic compass needles.

For example, young loggerhead turtles read the Earth’s magnetic field to adjust the direction in which they swim. The moment they hatch from eggs, they seem to know exactly where they are going, as if they were born with a set of directions, which, with the help of their magnetic sense, ensures that they always stay in warm waters during their first migration around the rim of the North Atlantic. Over time, they build a more detailed magnetic map by learning to recognize variations in the strength and direction of the field lines, which are angled more steeply towards the Poles and flatter at the magnetic equator.

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SCIplanet is a bilingual edutainment science magazine published by the Bibliotheca Alexandrina Planetarium Science Center and developed by the Cultural Outreach Publications Unit ...
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