My Science School

          Kangaroo rats are unique animals that live in desert and dry, open areas. They are perfectly adapted to desert life, and can survive without drinking water, as they get moisture from their seed diet.

          But, what makes kangaroo rats special is their exceptional sense of hearing. It helps them detect enemies like owls and snakes, even when they are approaching from a distance.

          Kangaroo rats have large ear-drums and middle ears. However, the oval window between the middle and the inner ears is considerably smaller. This peculiarity helps the auditory system of the animal to magnify low frequency sounds by about 100 times.

          As a result, it can hear the sound of air flowing over the wings of an owl, or the scales of a snake moving across sand. Now, isn’t that a rare gift for an animal?

 

          The barn owl is a raptor that can be spotted on all continents except Antarctica. It is said to have extraordinary abilities that help in catching fast-running animals.

          The most predominant ability is the bird’s sense of hearing, which stands out for its sharpness. It is so superior that the bird can decipher the direction and height from which a sound comes! This is exactly what makes it a sharp hunter.

          Unlike others, the barn owl’s ability to hear is strengthened by its feathers. The heart-shaped facial disc made of stiff feathers helps the owl in picking up noise. It funnels any sound towards the ears, which open on either side of the bird’s head. The ruff of feathers is so important for this owl that without it, the bird cannot catch preys. And with it, even the slightest sound can be detected.

          Interestingly, a large portion of the barn owl’s brain is devoted to building sound maps of places!

          Bats are fascinating animals that have many unique features. One of these is the ability to sense a prey location using sound. Confusing, isn’t? Let’s get to know how they do it.

          Bats use the sound technique known as ‘echolocation’. It means determining the location of something by measuring the time it takes for an echo to return from it.

          As they fly, bats make calls, and listen to the returning echoes to build up a sound map of their surroundings. These sounds are produced by contracting their larynx. Measuring the time it takes for the echo to return, this smart mammal can predict at what distance its prey is!

          Usually, the calls of bats are pitched at such high frequencies that humans fail to hear them naturally. Another interesting fact is that bats can distinguish between obstacles and preys through echolocation, and can thus avoid the obstacles and catch the prey.

          How many of us have seen birds that don’t make sounds? Not many. Birds are in fact, most known for their ability to make sound, be it sweet chirping, or harsh caws.

          While humans and other mammals produce sound from the voice box or larynx, birds have a different organ for sound production - the syrinx. Located near lungs, it is a double voice-box that consists of a resonating chamber, and numerous membranes. As air flows over them, the membranes move back and forth, producing sound.

          There are different frequencies at which bird sounds come out. There are other birds too that can sing in high frequency ranges, like warblers, sparrows, wax-wings, kinglets etc. It is believed that one can never stop a bird from learning its own species’ song.

          Interestingly, many species have at least some mimicked sequences in their most common songs and calls.

               For a long time, it was believed that oceans were silent places. But, as science advanced, it was proved that most of the animals living in waters cannot survive without sounds. 

               We know for a fact that light reaches only till the surface of water. In the case of smell, it fails to spread far from their source, while under water. Contrary to this, sound waves find their ideal medium in water, and travel faster than in air. They move greater distances, and at the surface of water, get reflected back into the depths. That is why even the sound of surf crashing on to a rocky beach travels far into the ocean.

               In general, sounds help most marine animals to sense their surroundings, communicate, locate food, and protect themselves.

               Mammals like whales, for instance, identify objects like food and obstacles using low frequency pulse signals. Dolphins communicate through clicks and whistles. They use the technique of echolocation to detect and characterize objects.

 

          Sounds become part of a bird’s life from the very moment they are born.

          It is wrong to think that the only sounds made by birds are songs. There are a variety of others too, like alarm calls, begging calls, contact calls, flight calls etc., used by them, depending on the circumstances.

          Songs are of course the most distinctive and familiar sounds. They are used mainly to attract mates, mark their territories, or discourage intruders. The quality and duration of a song depend on the species. Some may have different songs for different times of a day, but some sing only in the morning or evening. The yellowhammer, for instance, repeats its song around 1000 times a day.

          Begging calls are usually made by young birds to draw attention. Contact calls, on the other hand, are used to signal one another, particularly while travelling in a flock.

          In addition, there is something called the dawn chorus. It occurs when a large number of birds sing at the start of a new day. This is done either to protect a territory, or to call in the flock.

 

          Whales are in general, highly social creatures that move under water in groups called ‘pods’. To communicate and socialize with each other, they use different kinds of sounds; namely, clicks whistles and pulsed calls. Let’s see what these sounds are, and how they help the marine mammals.

          Clicks are made by whales for purposes of navigation and identification of physical surroundings. They also help to distinguish between friendly creatures and enemies.  

          The other two sounds- whistles and pulsed calls- are exclusively used during social interactions. The latter which are similar to squeaks, or screams, is rather more frequent.

          Surprisingly, there are differing vocal dialects existing between different pods. Perhaps this is why whales can differentiate between familiar whales and stranger whales.

          In addition to the above mentioned sounds, the marine mammals also make loud slapping sounds on the surface of the water, using tails and fins. This can be heard for very long distances, and are thought to be warning signs, or a tool to scare other smaller fishes. 

               The list of the best ‘singers’ among mammals can never be complete without humpback whales. These aquatic animals are capable of producing complex series of sounds that are close to songs. The whale songs, as they are popularly called, consist of a variety of loud, low-pitched tones, moans, whines and grunts that are often melodious in nature.

               But most importantly, the songs have themes that are sung in a precise order, and change slowly over years.

               The songs typically last 8-15 minutes, and are repeated for several hours at a stretch.

               Unlike other ‘singers’, humpback whales do not produce sound through vocal cords, simply because they don’t have any. Their songs are created when air is pushed out of the blowhole located on top of the animal’s head.

               Interestingly, some male humpbacks, like the North Atlantic ones, can be heard singing the same song together even when they are miles apart. 

            For deep vibrations and low frequency sounds waves to travel thousands of kilometres under deep sea, there has to be some path to save them from diminishing. Else, a phenomenon like whale communication will never be complete. It is in this context that the SOFAR channel gains relevance. Technically, it stands for Sound Fixing and Ranging and allows low-frequency sound to travel great distances.

            Let’s try to understand the concept better. Some of you might know that sound waves are highly dependent on medium, salinity, temperature and density. That is, at different pressures or temperatures, the waves will travel at different speeds. At a lower temperature in water, the waves move slowly, but at a higher pressure, they speed up. This causes the phenomenon in a level of the ocean called the SOFAR layer or channel.

            The advantage of this channel is that it allows sound waves to move without dissipating much of their energy. And if there is no energy drop, it means a wave can travel longer distance. 

          The howler monkey is a large type of monkey that can be spotted in the rainforests of South and Central America. Its strange name comes from the fact that its calls are louder than any other types of monkeys.

          There are quite a few kinds of sounds produced by the howlers. This includes loud grunts, roars, and barks and of course, howls. The monkeys are most vocal at dawn and dusk. A troop’s cries give information about their size and location.

          Now you may wonder how loud howler monkeys are. In fact, they are believed to be the loudest animals in the world. When a troop gets together and start howling, barking and grunting, the sound can be heard up to 4.8 kilometres away!

          What helps them produce such loud calls is the hyoid bone. This is a structure located near the neck that looks like a horseshoe in humans, but in howler monkeys, they are larger and more cup-like. It allows the animal to produce a single roar that lasts for about 8 seconds. 

            Drums are percussion instruments that have a thick membrane or skin, stretched tightly over its hollow body. They have been used for a long time, and are played with sticks, mallets, or hands. When the instrument is struck, the skin gets pushed down. It then starts vibrating, going up and down multiple times in a second. When this vibration pushes the air, sound waves are created.

            There are many factors that affect sound production in drums. If the head portion of the instrument is large, it produces a low-pitched sound. With a large body, drums absorb higher frequency sounds, while amplifying lower frequencies. As a result, a warmer tone will be produced. If the body is small, the sound generated will be sharp and bright.

            Another important consideration is the volume of air inside a drum. The higher the volume, the lower will the notes be. A further factor is the way with which the instrument is struck. 

              Wind instruments are those musical instruments that produce sound when air is blown into or across its mouthpiece. There are a variety of them used by musicians since time immemorial. The list includes flute, saxophone, clarinet etc. Many of them look similar with long tubes of various sizes and metal keys that cover the holes when played to make notes. In general, bigger instruments produce low pitched sounds.

               Depending on the material with which they are made, wind instruments are divided into two- brass instruments and woodwind instruments. In the former, sound is produced when the player’s lips vibrate, which in turn causes air inside the instrument to vibrate too. Examples of this are horns and trumpets.

              In the case of woodwind instruments, there are different ways with which sound is generated. Let’s look at an example of the most popular one- the flute. Here, an amount of air is gradually blown through the small mouthpiece. When this column of air gets trapped within the instrument, it vibrates, and produces the beautiful sound. There are of course factors that influence the final output.

 

          String instruments are those which make notes by vibrating. The best examples are the guitar, violin, piano etc. To play them, one has to make the strings vibrate by striking, plucking or rubbing a bow against them.

          Generally, string instruments have something called a sound box or resonator, which amplifies the sound. Each of them, however, works in their own way. For example, a guitar produces sound when the player plucks the string, either using a finger, or a piece of plastic called plectrum. The length of the string is fixed, and controlled by the player himself.

          There are different factors influencing sound in a string instrument, and the most important ones are length, weight, and tightness. If the strings are long, the vibration created would be slower, making lower sounding notes. 

            Electronic music generally refers to music created using electronic equipment. That is, any sound created by the means of electrical signals could be called electronic.

            Production of such music involves the use of power amplifiers as well as loudspeakers. Instruments such as synthesizer and electronic organ are examples of this. In these, oscillators produce electric signals with same frequencies as musical notes. The signals are then pushed to loud speakers. Subsequently, they cause the loudspeaker to vibrate, and produce musical sounds.

            History records that the earliest electronic equipment was invented sometime in 1897. It was called the teleharmonium, believed to have been developed by Thaddeus Cahill. But since it weighed around seven tonnes, the instrument was inconvenient for use. The first practical electronic musical instrument is considered to be the theremin, invented by Leon Theremin in 1919 - 1920. Since then, many more equipments have been developed till date. 

            Acoustics is the branch of science that deals with the production, control, transmission, reception and effects of sound.

            The word ‘acoustics’ has come from the Greek term akoustikos, meaning ‘for hearing’.

            Let’s see why acoustics is relevant. When a concert hall or a theatre is built, the architect needs to plan how sound waves travel through the air, so as to make sure everyone hears the same sound, clearly.

            Here, sound may be balanced using soft absorbent materials like curtains, carpets, plaster etc. Next, take the case of a doctor. He uses high pitched ultrasound waves in order to see the interiors of the human body.

            The wonders of acoustics have been seen in the world since centuries. The Greeks were known to be one of the earliest users of this technology.

            Today, there are many examples that demonstrate acoustics. One such is the Sydney Opera House in Australia.