Animals In Print
The On-Line Newsletter
From 11 August 2004 Issue
The wild side of animal senses
Beyond the five human senses
Radar, compasses, and infrared detectors are all man-made contraptions that enable humans to stretch beyond our natural senses. They allow us to see things in our environment that we otherwise could not see. But these gadgets are far from original. An examination of the sensory world of animals reveals that nature invented them long before we did.
About animal senses
Our senses tell us what we need to know about our environment. They help to keep us out of danger and enable us to find food and shelter. As humans, our senses include sight, sound, taste, smell, and touch. But other animals need different information about the world to survive than we do. As a result, they can have senses that are very different from our own: echolocation, infrared vision, electric sense, and magnetic sense.
Toothed whales (a group that includes dolphins), bats, and some shrews use echolocation to navigate their surroundings. Each of these animals emits high-frequency sound pulses and, in turn, detects the echoes produced by those sounds. Special ear and brain adaptations enable them to build a three-dimensional picture of their surroundings, much like radar. Bats, for example, have enlarged ear flaps that gather and direct sound towards thin, supersensitive eardrums.
Rattlesnakes and other pit vipers use their eyes to see during the day. But at night they use infrared sensory organs to detect and hunt warm-blooded prey. These infrared "eyes" are cuplike structures that form crude images as infrared radiation hits a heat sensitive retina.
Electric fields are used in numerous ways by animals. Electric eels and some rays have modified muscle cells that produce an electric charge strong enough to shock and sometimes kill their prey. Other fish use weaker electric fields to navigate murky waters or to monitor their surroundings. For instance, bony fish and some frogs have a lateral line, a row of sensory pores in the skin, that enables them to detect electrical current in water.
Together, 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. Amazingly, a number of animals are able to sense this magnetic field. Just as a compass helps us navigate by detecting magnetic north, animals who possess magnetic sense are able to identify direction and navigate long distances. Behavioral studies have revealed that many animals including honey bees, sharks, sea turtles, rays, homing pigeons, migratory birds, tuna, and salmon all have magnetic sense. The details of how these animals actually feel the earth's magnetic field is not yet known. Researchers have found, though, that each of these animals has deposits of magnetite in their nervous systems. Magnetite, small magnet-like crystals, align themselves with magnetic fields and might act like microscopic compass needles. These crystals may be the key to revealing how animals sense magnetic fields.
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