HUMAN HEARING AND NATURE’S APPLICATIONS Section 10.1 and 10.7

For a prize?  What does SONAR stand for?  SOund NAvigation and Ranging

Echolocation  Using echoes to locate an object  Use a variety of frequencies (40 kHz – 130 kHz)  Dolphins  Nasal sacs make high-frequency sounds.  Sounds pass through the “melon” Oval-shaped sac that is filled with acoustical lipids that focus the sound waves  Echo is received by a fat-filled cavity in lower jaw  Only good for ~ 5m - 200m (High frequency sound)  Vibrations are conducted to an auditory nerve and are perceived by dolphin much the same as sound in humans.  video

Elephants  Extremely intelligent  Large portion of their brain devoted to hearing.  Large pinnae  Used mostly for cooling and threat display  Have hearing receptors in trunks and feet  Produce sound from 15Hz – 35Hz up to 117dB  Long distances  video

Bats  Of the some 900 species of bats, more than half rely on echolocation to detect obstacles in flight, find their way into roosts and forage for food.  Most bats produce echolocation sounds by contracting their larynx (voice box).  A few species, though, click their tongues.

 sounds are generally emitted through the mouth, but Horseshoe bats (Rhinolophidae) and Old World leaf-nosed bats (Hipposideridae) emit their echolocation calls through their nostrils: there they have basal fleshy horseshoe or leaf-like structures that are well-adapted to function as megaphones.

 calls are usually ultrasonic--ranging in frequency from 20 to 200 kilohertz (kHz)  human hearing normally tops out at around 20 kHz.  In general, echolocation calls are characterized by their frequency; their intensity in decibels (dB); and their duration in milliseconds (ms).  Video – what does this sound like?

pitch  bats produce echolocation calls with both constant frequencies (CF calls) and varying frequencies that are frequently modulated (FM calls).  Most bats produce a complicated sequence of calls, combining CF and FM components.  Although low frequency sound travels further than high-frequency sound, calls at higher frequencies give the bats more detailed information--such as size, range, position, speed and direction of a prey's flight.

 bats emit calls as low as 50 dB and as high as 120 dB, which is louder than a smoke detector 10 centimeters from your ear.  That's not just loud, but damaging to human hearing. The Little brown bat (Myotis lucifugus) can emit such an intense sound.  The good news is that because this call has an ultrasonic frequency, we are unable to hear it.

Too cool!  The ears and brain cells in bats are especially tuned to the frequencies of the sounds they emit and the echoes that result. A concentration of receptor cells in their inner ear makes bats extremely sensitive to frequency changes: Some Horseshoe bats can detect differences as slight as.000l Khz. For bats to listen to the echoes of their original emissions and not be temporarily deafened by the intensity of their own calls, the middle ear muscle (called the stapedius) contracts to separate the three bones there--the malleus, incus and stapes, or hammer, anvil and stirrup--and reduce the hearing sensitivity. This contraction occurs about 6 ms before the larynx muscles (called the crycothyroid) begin to contract. The middle ear muscle relaxes 2 to 8 ms later. At this point, the ear is ready to receive the echo of an insect one meter away, which takes only 6 ms.

Owls  An Owl's range of audible sounds is not unlike that of humans, but an Owl's hearing is much more acute at certain frequencies enabling it to hear even the slightest movement of their prey in leaves or undergrowth.

 Some owl species have asymmetrically set ear openings (i.e. one ear is higher than the other) - in particular the strictly nocturnal species, such as the Barn Owl or the Tengmalm's (Boreal) Owl.  These species have a very pronounced facial disc, which acts like a "radar dish", guiding sounds into the ear openings. The shape of the disc can be altered at will, using special facial muscles!

Barn owl

Boreal Owl

 Also, an Owl's bill is pointed downward, increasing the surface area over which the soundwaves are collected by the facial disc. In 4 species (Ural, Great Gray, Boreal/Tengmalm's & Saw-whet), the ear asymmetry is actually in the temporal parts of the skull, giving it a "lop-sided" appearance.

Northern Saw-whet Owl

Great gray owl skull

 Owls listen for prey movements through ground cover such as leaves, foliage, or even snow.  When a noise is heard, the Owl is able to tell its direction because of the minute time difference in which the sound is perceived in the left and right ear - for example, if the sound was to the left of the Owl, the left ear would hear it before the right ear.  The Owl then turns its head so the sound arrives at both ears simultaneously - then it knows the prey is right in front of it.  Owls can detect a left/right time difference of about seconds (30 millionths of a second!)

House Cats  Excellent hearing (from 55 Hz – 79 kHz)  Large, moveable pinnae  Amplification and directionality of sound.  Make up for poor vision with their excellent hearing.  Seeing well in the dark sacrifices some colour vision

On the offense?  hard to believe that animals can in fact use auditory signals to harm other animals.  The bottlenose dolphin uses echolocation frequencies that can be over ten times our upper hearing of 20 kHz. Some high-intensity click sounds (230 dB) by bottlenose dolphins, beaked whales, and sperm whales may serve to debilitate prey by overloading fish lateral lines, ears, or shattering bony ossicles and other tissue.

10.7 Summary  Natural phenomena can be explained with reference to the characteristics and properties of sound waves.  Dolphins, sperm whales, and orca whales use echolocation to navigate and detect prey in dark, murky waters.  Bats also use echolocation to detect prey.  Elephants produce infrasound waves, which travel partially through the ground. They can detect these sounds with their feet and trunks pressed against the ground.  Cats use their large movable pinnae to amplify sound and to detect the direction from which sounds are coming.