4 Senses Animals Have That Humans Don't

Radar guns, magnetic compasses, and infrared detectors are all man-made inventions that enable humans to stretch beyond the five natural senses of sight, taste, smell, feel, and hearing. But these gadgets are far from original. Evolution equipped some animals with these "extra" senses millions of years before humans evolved.

Echolocation

Toothed whales (a family of marine mammals that includes dolphins), bats, and some ground- and tree-dwelling shrews use echolocation to navigate their surroundings. These animals emit high-frequency sound pulses, either very high-pitched to human ears or completely inaudible, and then detect the echoes produced by those sounds. Special ear and brain adaptations enable these animals to build three-dimensional pictures of their surroundings. Bats, for example, have enlarged ear flaps that gather and direct sound toward their thin, super-sensitive eardrums.

Infrared and Ultraviolet Vision

Rattlesnakes and other pit vipers use their eyes to see during the day, like most other vertebrate animals. But at night, these reptiles employ infrared sensory organs to detect and hunt warm-blooded prey that would otherwise be completely invisible. These infrared "eyes" are cup-like structures that form crude images as infrared radiation hits a heat-sensitive retina. Some animals, including eagles, hedgehogs, and shrimp, can also see into the lower reaches of the ultraviolet spectrum. Human beings are unable to see either infrared or ultraviolet light with the naked eye.

Electric Sense

The omnipresent electric fields produced by some animals function like senses. Electric eels and some species of rays have modified muscle cells that produce electric charges strong enough to shock and sometimes kill their prey. Other fish (including many sharks) use weaker electric fields to help them navigate murky waters, home in on prey or monitor their surroundings. For instance, bony fish (and some frogs) possess "lateral lines" on either side of their bodies, a row of sensory pores in the skin that detect electrical currents in the water.

Magnetic Sense

The flow of molten material in the earth's core and the flow of ions in the earth's atmosphere generate a magnetic field that surrounds the planet. Just as compasses point humans toward magnetic north, animals possessing a magnetic sense can orient themselves in specific directions and navigate long distances. Behavioral studies have revealed that animals as diverse as honey bees, sharks, sea turtles, rays, homing pigeons, migratory birds, tuna, and salmon all have magnetic senses. Unfortunately, the details about how these animals actually sense the earth's magnetic field are not yet known. One clue may be small deposits of magnetite in these animals' nervous systems. These magnet-like crystals align themselves with the earth's magnetic fields and may act like microscopic compass needles. 

Edited by Bob Strauss