Category Science

               The twittering of birds usually produces a pleasant sensation, especially in the spring in countryside. Some birds produce very sweet sounds while others produce harsh and unpleasant sounds. Do you know why birds sing?

               The songs and calls are important methods of communication among birds. They sing to attract mates in the mating season, to warn other birds of any incoming danger from predators, and to establish their home territories or nesting area. The bird calls are usually distinctive and vary from species to species. This distinction helps the birds to identify the calls meant for them.

               Among all the species of the singing birds, the male bird is usually the singer. It sings to attract the female bird. The songs of nightingale produce the best musical effects and other birds do not match it in comparison. The mocking bird has its own harsh call but can imitate the songs of other birds. Crow has a very crude voice.

                Apart from singing, birds make other types of calls — call for sending alarm signals, for food or calling their parents, call in an aggressive or hostile mood etc. A few birds, such as pelicans and cormorants, are voiceless.

               The singing birds belong to the suborder oscines. Their vocal cords are located in a special box, the syrinx, at the base of the windpipe where it divides into two bronchi. The syrinx has a bony structure and forms a sound-box within which membranes vibrate when the bird exhales. This produces varying notes in the bird’s voice. The structure of syrinx varies from species to species and till now seven different types have been recognized.

               The songs of the birds have a pitch of about 4300 Hertz, which is above the highest note of a piano. Intensity of the calls of any single bird varies from the deep-pitched hoot of owls to the very high notes of small birds which are scarcely audible to the human ear. 

            There are several species of birds on earth which cannot fly because they stopped using their wings for flying many thousands of years ago. Perhaps neither the environment around them nor their living conditions required them to fly. Generally birds fly either to protect themselves from enemies or in search of food. These flightless birds either lived in places where there were no enemies to prey on them, or were so big that they could rely on their legs to carry them out of trouble. As a result, their wings almost fell into disuse and gradually they became flightless. Do you know which are the birds that cannot fly? 

        First of all we have the Penguins. They turned their wings into paddles or flippers. As a result they cannot fly but they are excellent swimmers. These birds mainly live in the southern hemisphere – mostly at the edge of Antarctica. 

                The Kiwis of New Zealand took to living by night, finding its food by smell and almost ceased flying. Gradually the bird became flightless. Also it almost stopped using its eyes and today it has very poor eyesight. Now these birds have small wings which are hidden by hair-like feathers that cover the body. 

Continue reading “Which birds cannot fly?”

               The most surprising fact about fishes is that you cannot hear them but, they can certainly hear you. Fishes are very well-equipped for hearing. They have a pair of ears. These ears do not have an outer projection as we have, but are simply tiny holes on either side of the head, leading to the inner ear. Since there is no external ear to direct the sound, these ears are probably not as effective as our own. But the fishes have other ways of picking up sounds of vibrations in the water. 

              Along each side of the fish’s body is a line of little holes or pores, which can also pick up vibrations and changes in pressure inside water and pass on the message to the brain. This line of pores is called the lateral line, and can be seen quite easily.

               By using this lateral line a fish can avoid all obstacles when it is extremely sensitive to pressure changes caused by the vibrations of another fish or some other objects. A fish’s lateral line contains sensory cells which provide the fish with all the information of events going on around it.

                   Some other teleost fishes such as catfish that lives in rather muddy water have barbells — long sensitive feelers on their mouths.

                   The fishes of the ‘carp’ family have tiny bones in the head which are linked to the swim bladder. The swim bladder keeps the fish upright in water and also acts as a sounding board which can pick up and magnify the tiniest vibrations, and then pass them along the bones directly to the inner ear.

                   These are the different mechanisms in the fishes by which they can even hear very feeble sounds. 

                There are certain peculiar types of bugs called ‘Back Swimmers’ (Greater-water Boatman) that can swim upside down. These back-swimmers are also called boat bugs. Although they spend most of their lives in water, they are able to fly long distances. These insects are small, usually 3 to 17 mm (0.13 to .63 inch) in length. Instead of wings they use their legs to swim. They swim on their backs and make use of their hind legs to paddle through the water. These flat ‘paddles’ are ideal for swimming, and are often made even more efficient by a fringe of hairs which runs down each side. This makes a broader surface to push against the water. The insect uses its short front legs for holding the prey.

                Back swimmers hold a bubble of air between their wings and body. This air is used for breathing when they are underwater. This lets them stay underwater for as long as six hours. In winter, back swimmers bury themselves in the mud at the bottom of a pond or stream.

                They have sharp beaks which they use for stabbing fish and other small water animals and suck out their juices. Back swimmers sometimes even bite human beings.

                These creatures belong to Notonectidae family which has in all about 200 species. They are found generally all over the world. They cause great harm to fishes and tadpoles. They deposit their eggs in the plant tissue of pond vegetation. 

                    When a cat wants to express contentment or pleasure, it purrs. Purring of a contented cat results in a low vibrating noise. It is a kind of low, continuous rattling hum and has nothing to do with a cat’s real voice. A mother cat purrs when it wants to call her kittens for feeding. At birth the kittens cannot see, hear or smell. So in the initial stages after birth, it is the purring of their mother that helps them to communicate with her. Once the kittens start feeding themselves, the mother stops purring. It implies that purring began as a kind of homing device.

               Now the question arises how a cat produces the purr? 

               Purr is caused by the vibrations in a cat’s vocal cords. When a cat takes air into its lungs, the air passes through the voice-box that contains the vocal cords. If the cat then wants to express its satisfaction about something, it will allow the vocal cords to vibrate as the air passes in and out of the lungs during breathing. When it chooses not to purr, the passing air does not affect the vocal cords and thus doesn’t produce any such sound.

                Although there are many other members of the cat family such as lion, tiger, leopard, cougar, jaguar, ocelot and lynx, their throat structure is quite different from a cat and hence they cannot purr. However, they can make other kinds of sound.

               It is said that only man has highly developed reasoning faculties and hence can think and act accordingly. But there are animals that sometimes, with their superior senses excel man in certain activities. For example, dog has an excellent power of smell and often helps man in his day-to-day life. Like man there are some animals who take reasonable care of their offspring. But how do these animals recognise their young ones?

               Among the animals where parental care is prevalent, it is important for the mother and her young ones to recognise one another, so that they do not lose contact. This is done through one of their four senses: smell, sound, sight or touch.

               Most of the mammals recognise their offspring by smell. It is a common practice among dogs, deer, sheep, horses and seals.

               It’s interesting to note that among a flock of sheep every mother can recognise her own young ones by smell and ignore others. Among some other animals, when a young one is born, its mother sniffs it and the smell remains in her memory. Thereafter the mother easily locates her baby by sniffing all the babies around until she finds her own.

               Among the birds recognition is more by sound. Each parent bird has her own special ‘mother call’ which the baby immediately recognizes on hatching. An Austrian naturalist, Dr. Konard Lorenz, has made a special study of geese. He conducted his study just before some gooslings were about to hatch. He immediately removed the mother goose and sat by the eggs himself. As the babies hatched he gave the ‘mother call’. As a result, they followed him everywhere believing him to be their mother as they recognized only the sound. But since he was too big for the young geese they got confused when he stood up. However they were quite happy to follow him when he crawled about on hands and knees.

               To some animals, shape and size also matter as the sense of touch also plays an important role in the recognition of young ones.