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SENSEsational (Fall/Winter, 1993)
Making Sense of the Senses Shorebirds and Fish Hawks and Bats Changes to the State List of Threatened and Endangered Species

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Why do snakes continually dart their tongues in and out? They're smelling the air and ground with their tongues! The tip of the snake's forked tongue picks up molecules of chemicals which are sampled by the Jacobson's organ, a scent organ in the roof of the mouth.

Bears are renowned for their sense of smell. Bears have entered tents where there is no food, attracted by the clothing which had been carried in a pack with food.

Members of the dog family have a highly acute sense of smell, as any dog owner can tell you. From nine feet away, foxes can scent food buried four inches deep. A German shepherd s sense of smell is estimated to be one million times better than a human s. How does a dog remember and identify all the scents it encounters? Dogs probably process smells in the same way humans sort out all the visual information with which we are constantly bombarded. We "view" our world through visual images, while a dog "sees" the world largely through "scent images". We accept most of the colors and shapes we see as fitting into an expected picture, without needing to think, "That's green grass, there's a moving car". We only react to something out of the ordinary. Dogs probably do the same with scents, ignoring familiar smells while paying attention to something new or particularly interesting "Whoa, some newcomer left his mark on my bush!"

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Humans are highly visual, but we are outdone by some animals. Not only can owls see in what we perceive as total darkness, but they probably see better than we do during the day. Feathery disks around the face help reflect light into their huge eyes, which are the size of a human s, but 100 times more acute. Thus, an owl can discern a mouse in the grass, with a high degree of clarity and detail, at probably five times the distance at which a human begins to distinguish an object from its background.

A vulture can see an animal carcass on the ground while soaring at heights up to 2.5 miles, distances at which humans can't even see the bird in the air! The vulture has a concentration of one million cones (photoreceptors which perceive color and detail) per square millimeter in its eye, at least five times that of humans.

Diving birds like cormorants and mergansers can squeeze the shape of their lens to overcome the distortion of light underwater. Many birds have colored oil droplets in their eyes which act as filters to highlight certain colors. This may help them perceive polarized light and see through fog.

Snakes of the pit viper family, like rattlesnakes, have pits on the sides of the head that sense infrared radiation (heat). Thus, they detect warm-blooded prey by "seeing" the warmth they radiate. Infrared sensors, or "eyes", inside the mouth help the snake zero in accurately as it strikes its prey.

Most lizards in Colorado have a "parietal eye" on top of the head; it has a lens and retina, but can't register an image. This "eye" probably acts like a light meter to control the amount of time the lizard spends in the sun.

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If humans could hear in the ultrasonic (literally "beyond sound") range, we would probably go "batty", constantly bombarded with noise-the roars of bats, the humming of insects, the squeaks, rustles, chirps, and shouts of a world of sound.

Coyotes and foxes are known to hunt by sound, their large ears directed like radar dishes, listening for the rustle of mice and other prey in the grass and snow. Canids (members of the dog family) can hear frequencies up to 40,000 cycles per second (compared to 20,000 cps in humans), so they're catching all those high-pitched noises we miss, a fact which never ceases to amaze dog owners.

Though the range of hearing in most birds is less than humans, the cochlea of their middle ear responds to sound 10 times faster than ours. Owls, of course, are champion hearers. Barn owls accurately locate mice in total darkness to within a fraction of an inch, completely by sound. One ear is set higher than the other, so the bird can pinpoint sounds both horizontally and vertically. Moving its head to equalize sound, the owl aligns the source with its line of vision. A little squeak, a little scurry, and whammo, a mouse is done in by an ear with talons.

And while the predators are listening, so are their prey. The kangaroo rat, a nocturnal rodent of deserts and prairies where there is little cover, has acute hearing. Its inner ear magnifies sounds nearly 100 times. Studies found that kangaroo rats put in a cage with an owl leaped straight up and out of the way every time the owl struck, leaving the bird clutching air. When its middle ear was blocked, the rat was a goner.

As they explore, shrews utter a high-pitched twittering. Like bats and dolphins, they use echolocation to find food and detect obstacles.

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Living in a dark, subterranean world, moles, shrews, and pocket gophers have little use for eyes. Instead, they gather information with their highly sensitive whiskers, feeling their way along dark tunnels. Moles have conical bumps on the tips of their hairless snouts which are rich in nerve endings and blood supply and highly sensitive to touch and temperature change. Fitting fairly tightly in their burrows, like a piston in a cylinder, moles may be able to feel changes in air pressure and movement as they encounter obstacles, prey or other moles. They also detect the movements and digging of worms by vibration. Gophers have tactile nerve endings in their hairless tails to help them feel their way when they put it in reverse.

Cats have a fan of whiskers around the face. These are certainly useful tools for an animal prowling at night, poking its curious face towards anything interesting. The same nerve path carries information from the whiskers and the eyes, which work in concert to give the cat a 3D picture of its world.

Look at a trout and you'll see a line running down each side of the body, from head to tail-the vibration-sensing lateral line organ. Small pores in the skin along this line open to hairlike receptors which are very sensitive to changes in water flow and pressure. This distant-touch sense is used to detect prey, avoid predators, maintain school formations, and communicate with other fish of the same species. The lateral line system could be an evolutionary precursor to hearing.

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Do some animals have a "sixth sense" humans lack? Folklore credits animals with sensing earthquakes and changes in weather before people do. They are very likely more sensitive to the earth's vibrations and changes in barometric pressure than humans. Perhaps they "predict" impending storms by sensing the electromagnetic energy given off by distant thunderstorms. The use of the earth's magnetic field for navigation by birds is well documented, though we still aren't sure how they sense it.

Next: Shorebirds and Fish

(The information contained in these issues of Colorado's Wildlife Company was accurate at the time of original publication. Situations and circumstances described, staff positions, contact information, and dates of some events may have changed in the interim. Present knowledge and understanding of biological and behavioral facts and information may also be different, now, than presented here.)