The range of colors our eyes capture is but a minute fraction of the electromagnetic spectrum. For instance, our eyes cannot see infrared radiation, which has a longer wavelength than red light. However, pit vipers have two small organs, or pits, between their eyes and nostrils that detect infrared radiation.Hence, even in the dark they can accurately strike at warm-blooded prey.
Beyond the violet end of the visible spectrum is ultraviolet (UV) light. Although unseen to our eyes, UV light is visible to many creatures, including birds and insects. Bees, for instance, orient themselves in relation to the sun
Because birds see in the UV range and because this light gives their plumage extra radiance, birds probably look more colorful to one another than to us. They have a visual “depth of richness that we can’t begin to imagine,” said one ornithologist. The ability to see UV light may even help certain hawks and kestrels to locate voles, or field mice. How so? Male voles, says the journal BioScience, “produce urine and feces containing chemicals that absorb UV, and mark their trails with urine.” Thus, birds can “identify areas of high vole density” and focus their efforts there.
Why Do Birds See So Well?
Bird vision is a marvel. “The chief reason,” is that the image-forming tissue lining the eye’s interior is richer in visual cells than the eye of other creatures. The number of visual cells determines the ability of the eye to see small objects at a distance. While the retina of a man’s eye contains some 200,000 visual cells per square millimeter, most birds have three times that number, and hawks, vultures, and eagles have a million or more per square millimeter.” Additionally, some birds have the extra asset of two foveae
The Electric Sense
The scenario mentioned earlier involving the hidden flounder and the shark actually occurred during a scientific study of sharks. The researchers wanted to know if sharks and rays sensed the minute electric fields that emanate from living fish.To find out, they hid electrodes in the sandy floor of the shark pool and applied the appropriate voltage. The result? As soon as the shark neared the electrodes, it viciously attacked them.
Sharks possess what is called passive electroreception; they sense electric fields just as the ear passively hears sound. But electric fish have active electroreception. Like a bat that emits an acoustic signal and reads the echo, these fish emit electric waves or pulses, depending on the species, and then, with special receptors, detect any disturbances made to these fields.Thus electric fish can identify obstacles, potential prey, or even a mate.
A Built-in Compass
Think what life would be like if your body were equipped with a built-in compass. Getting lost would surely not be a problem! Within the body of a number of creatures, including honeybees and trout, scientists have found microscopic crystals of magnetite, or lodestone, a natural magnetic substance. The cells containing these crystals are connected to the nervous system. Hence, bees and trout have demonstrated the ability to detect magnetic fields. In fact, bees use the earth’s magnetic field for comb building and navigation.
Investigators have also discovered magnetite in a species of bacteria that live in seafloor sediment. When the sediment is stirred up, the earth’s magnetic field acts on the magnetite to align the bacteria in such a way that they propel themselves safely back into their seafloor home. Otherwise, they would die.
Many migratory animals
Compared with humans, many creatures possess amazing hearing. Whereas we can hear sounds ranging from 20 to 20,000 hertz (cycles per second), dogs can hear in the range of 40 to 46,000 hertz, and horses, between 31 and 40,000 hertz. Elephants and cattle can even hear in the infrasonic range (just below human hearing) to as low as 16 hertz. Because low frequencies travel farther, elephants may be able to communicate over distances of two or more miles [4 km]. In fact, some researchers say that we could employ such animals to give us an early warning of earthquakes and severe weather disturbances
Insects also have a wide range of hearing, some in the ultrasonic range over two octaves above the human ear and others in the infrasonic range. A few insects hear by means of thin, flat, eardrumlike membranes, which are found on almost every part of the body except the head. Others hear with the aid of delicate hairs that respond not just to sound but also to the most gentle movements in the air, such as those caused by a human hand. This sensitivity explains why flies are so hard to swat!
Imagine being able to hear an insect’s footsteps! Such amazing hearing belongs to the world’s only flying mammal
Because precise echolocation also depends on the quality of the sound signal emitted, bats have the “ability to control the pitch of their voice in ways that would be the envy of any opera singer,” .Apparently by means of the flaps of skin on the noses of some species, bats can also focus sound into a beam. All these assets contribute to a sonar so sophisticated that it can produce an “acoustic image” of objects as fine as a human hair!
Besides bats, at least two kinds of birds
Sonar at Sea
Toothed whales also employ sonar, although scientists have yet to discover exactly howthis works. Dolphin sonar begins with distinct clicks, which are believed to originate, not in the larynx, but in the nasal system. The melon
Dolphin sonar clicks are strikingly similar to a mathematical waveform called a Gabor function. This function, says Hughes, proves that dolphin clicks “approach a mathematically idealized sonar signal.”
Dolphins can adjust the power of their sonar clicks from a mere whisper to a cracking 220 decibels. How powerful is that? Well, loud rock music can produce 120 decibels, and artillery fire 130 decibels. Armed with sonar that is much more powerful, dolphins can detect things as small as a three-inch [8 cm] ball 400 feet [120 m] away and possibly even farther in quiet waters.