My Science School

            Migration is a fascinating phenomenon that Nature repeats every year. It is the seasonal movement of some animals, from one place to another, year after year, usually across vast distances.

            Birds, fishes, mammals, insects and reptiles all migrate. Animals migrate for many reasons. It may be to find food, or to escape harsh weather. Some may travel thousands of miles in the spring, and then, thousands of miles back in the fall.

            Animals also migrate in search of better food supplies, or a safe place to give birth to their young. Such migrations happen on a regular basis. Irregular migrations are sometimes triggered by famine or over-population.

            The Arctic tern, the sea bird, travels from one end of the world to the other end every year! This is the longest migration undertaken by any bird. This bird flies in zigzagging routes between breeding grounds in the Arctic and Antarctica each year, a distance of around 70,900 kilometres. They will spend about four or five months in Antarctica, before heading back to the Arctic. Scientists have extensively studied the evolution of migration. But no single theory has been fully accepted.

            No, not all birds fly. The ostrich, the largest bird on Earth is the best example of a bird that cannot fly. The ostrich is found in the African savannah. Though it cannot fly, it can run very fast, at a speed up to 72 kilometres per hour. An ostrich may be as much as 2.5 metres tall and weigh about 135 kilogrammes. Ostriches produce the largest egg of any living bird. One egg may weigh about 1500 grammes and have the same volume as 25 hen eggs.

            Ostriches, penguins, cassowaries, rheas, emus and liwis are the most well-known flightless birds.

            The penguin, found in Antarctica, has wings modified into flippers to aid it in swimming.

            The cassowary is a large, flightless bird from Australia and New Guinea. It is the biggest bird in Australia, and the second biggest bird in the world, after ostrich. Cassowaries grow to be about 2 metres tall and weigh about 60 kilogrammes. The largest known cassowary was 83 kilogrammes. The cassowary’s life span is about 40 to 50 years.

            Cassowaries have powerful legs and a helmet like crest on the head. They protect themselves by kicking. Cassowaries can run at a speed of upto 50 kilometres per hour.

            Rheas are found only in South America. They are also called South America ostriches. These birds have a height of about 1.5 metres and weigh more than 25 kilogrammes. Rheas are brown in colour.

            Kiwis are small flightless birds. They are the size of a hen, and weigh from 1.5 to 4 kilogrammes. There are three types of kiwis – the common kiwi, spotted kiwi and the little gray kiwi. All are found in New Zealand.

            An important difference between flying and flightless birds is the fact that flightless birds have smaller wing bones. Another distinction is the absent (or greatly reduced, or flat) keel on the breastbone of flightless birds. Flying birds have a keel on their breastbone. The keel anchors the strong muscles that move a bird’s wings during flight. Flightless birds also have more feathers than flying birds. These feathers weigh more.

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            The fastest known bird in level flight is the white throated spine tailed swift. It has been recorded as flying at speeds of over 170 kmph.

            Common eiders, or coastal ducks, can fly nearly 75 kmph. Dunlins (shorebirds) once caught up with, and passed a plane flying at 160 kmph! Swifts, as their name indicates, are among the fastest of all flying birds.

            Peregrine falcons can chase their prey in level flight at 60 kmph, but when stooping or diving to catch it, they reach much higher speeds.

            Other high-speed birds include buzzards, which can glide between 110 and 130 kilometres per hour. Swallows are believed to be able to reach 160 kilometres per hour when migrating, but normally, they do not fly faster than about 50 kilometres per hour.

            The Andean condor, with a wingspan of up to 2.9 metres, is the largest flying bird! This bird lives in the Andes Mountains of South America. Both the Andean condor, and its slightly smaller cousin, the California condor, have unusual wings which allow them to soar only when there is an upward rising air current, and when the weather is dry. When it rains, condors cannot fly, so they must stretch out their wings and allow them to dry before they can once again take to the air. California condors are an endangered species.

            The wandering albatross is also a large flying bird. From one wing tip to another, it’s as long as a family car!

            To escape winter, the whooper swan flies nonstop from Iceland to Scotland – a 1125 km flight. This is the longest flight made by any species of swan. Whoopers are very shy birds, who got their name from the whooping calls they make. They are usually found in fresh water, though at times, they can be seen on sheltered inlets. There are only 1,00,000 Whoopers in the entire world, but their future is very secure, because it is against the law to kill them.

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               Colours in the feather of a bird are formed in two different ways. Pigments, and the physical structure of the feather. Many feathers are coloured by a combination of these features.

               Pigments are chemical compounds that absorb certain wavelengths of light while reflecting others. The colours you see are those reflected back. Feathers coloured by pigments range from crow black to canary Yellow and cardinal red.

               Many colours, such as blue, are a result of feather structure. When light hits these feathers, it hits microscopic structures on the feather that act as prisms to reflect a colour. No blue pigment is known in birds. If you crush a blue scrub jay feather, or dunk it in water it will appear gray.

               Shimmering iridescent colours such as those found in hummingbirds and peacocks are caused by special structures, air bubbles, or films in feather surfaces. These modifications interfere with the bending and scattering of light to strengthen some wavelengths, and cancel out others.

            Bird feathers, which evolved from the scales of reptiles, perform the same function that reptile scales do - they protect a bird in a variety of ways - from the harmful rays of the Sun, from rain, and from injury to their delicate skin.

            They also have the remarkable ability to trap air, thus insulating birds from the cold. There are also feathers on the wings of a bird, which help it to fly. Some birds also use their own feathers to line their nests. Ptarmigans, birds that live in the snow, have feathers on their feet that act like snowshoes!

            These special feathers help the birds from falling through deep snow. This bird changes its feathers three times a year, to help it to camouflage itself as the seasons change.

            The sand grouse, a desert bird, dips its feathers into water and then flies to its chicks, who suck the water off the feathers when they are thirsty!

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                     Yes, indeed! It is not wings, or beaks, or the ability to lay eggs that make a bird a bird. Some mammals lay eggs, and have beaks (like the duck-billed platypus), and some others can fly (like the bat). Reptiles like snakes and crocodiles also lay eggs.

                       However, it is feathers that differentiate a bird from other creatures. Birds are the only creatures that possess feathers.

                    It all started some 200 million years ago, when some smaller dinosaurs made their homes among rocks on high cliff sides. By doing this, they were protecting themselves from larger meat-eating dinosaurs that were too big and heavy to climb over loose rocks. It was here that the pterodactyls (meaning ‘wing finger’) were found. They were flying reptiles, and their ability to fly helped them to escape from the clutches of an enemy, and to swoop down to grab food.

                  During this period, many small reptiles were evolving characteristics, which separated them from the reptile group - their feathers. The Archaeopteryx was the most familiar of these early reptilian avian.

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                    About 9,000 different species of birds exist today in our world. They come in all sizes, forms, and colours. There are brightly coloured parrots and macaws in tropical America, and large cassowaries and emus that cannot fly in Australia. Tiny warblers and sparrows are found in temperate America, and ducks, bustards and cranes in India. Gulls and vultures soar through the skies the world over. Plump chickens and turkeys are found in farmyards everywhere.

                   There are two main bird groups- paleaeognathae and neognathae. The paleaeognathae, includes birds that first evolved during the Cenozoic Era, after the dinosaurs became extinct-mostly ratites such as ostriches, emus and kiwis. The neognathae can trace their roots much farther back into the Mesozoic Era, and includes all other types of birds.

               The number of fish species runs to more than 20, 000 in the entire world! They can be classified into three broad categories: bony, cartilaginous and jawless. These species are spread across various biospheres. Around 10,000 species are found in freshwater; whereas, around 20,000 live in saltwater. There are also fish species that can live both in fresh and salt Water.

               The most commonly found fishes fall in the category of bony fishes. Tiny bones make up the skeleton of these fishes. They also have scales all over their body. They breathe through gills that appear at both sides of their head.

                On the other hand, cartilaginous fish have skeletons made out of cartilage. Cartilage is a kind of flexible tissue, and it is less brittle than bone. Sharks and rays have cartilages instead of brittle bones. As you may have observed, sharks have several gill slits on either side of their heads. They do not have scales like fishes. However, they have little interlocking teeth that make up its tough skin.

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               If you carefully analyse the fish in your aquarium, you would see a skeleton inside its body. The parts of the skeleton are a skull, backbone and fin supports. The skull of a fish has a cranium, and visceral arches. The bony cover that surrounds, and protects the brain is called the cranium. The visceral arches in the body of a fish support of its gills. These arches are also called the gill arches.

               The backbone of a fish is series of disc like bones. The backbone protects the spinal cord of the animal. There are thin, needle-like ribs that extend from the backbone toward the belly. This structure supports the entire body of a fish.

               Many fins are found in the body of a fish. Each fin has a large support at its base. They have two sets of fins, which are paired. One pair is called the pectoral fins, which lie just behind the head, one on both sides; and the other pair is called the pelvic fins, which may be far back on the body or under the head. The pelvic fins are smaller than the pectoral fins and are always on the belly side of the fish. Other fins of the fish are generally un-paired. It means that there is only one of each. The dorsal fin is found at the centre of the back of the fish. Fishes have an anal fin on the belly side too, just in front of the tail. The tail of the fish is called the caudal fin.

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          Can you imagine rivers, lakes or great oceans without fishes? These animals make grand water bodies livelier. However, millions of years ago, there were no fishes in waters!

          Scientists who study fossils to place various prehistoric organisms say that the first fish probably came into existence about 500,000,000 years ago, in the Ordovician Period.

          The ancient fishes did not have the kind of mouth fishes have now. They were jawless. They just had a small opening as their mouths, with which they ate only tiny organisms found hidden in the mud. These fishes gradually evolved and spread in number to other bodies of water later. During the Devonian Period, fishes were the most common animals in the planet. Therefore, the period is also known as the age of fishes.

          Jawless fishes and fishes with jaws became abundant during this time. Ostracoderms were a group of jawless fishes. However, they soon became extinct.

          The jawless fishes died out because fishes with jaws were evolving. Early fishes with jaws are called Placoderms. Do you know that the sharks and bony fishes of the present day come from Devonian Placoderms?

                  Vertebrates represent the majority of life in the phylum Chordata. There are more than 65,000 species among vertebrates. Of these, the fishes constitute the majority. There are thousands of fish species across the globe. The fish diversity is spread across lakes, rivers, streams, seas, bays and oceans. They are found in the cold Arctic, in the hot tropics and in other temperate zones. When it comes to the number of species or individuals, fishes outnumber all other vertebrates.

                   Do you know that a scientist who studies fishes is called and an ichthyologist? The word comes from two Greek words: ‘ichthyos’, meaning fish, and ‘logos’, meaning study.

 

               Have you ever gone fishing in a lake or river? From time immemorial, fish has been close to Man either as food or pet.

               Like human beings, fishes have backbones. There is a general misconception among common people that all animals that live in water are fish. That is manifest in addressing certain animas such as shellfish, starfish and cuttlefish as fish. However, that is incorrect because they are evidently different from true fish. The previously mentioned animals are invertebrates-animals without backbones.

               There are mammals too. Whales and porpoises cannot be categorized as fish as they are mammals that have adapted to life in the sea. These animals cannot breathe underwater like fishes, as they have to come up to the surface to breathe.

               Fishes, therefore, are aquatic animals with vertebra that live and breathe in the water. They have special anatomical features that help them in water such as gills, fins and scales. These animals possess basic vertebrate features, such as a brain, eyes, ears, blood, muscles and bones.

            Snakes in India are treated with not only fear but also prayerful worship. However, many a species is in grave danger because of several reasons.

            The most important of them is deforestation. The felling of trees is a big blow to reptiles. Most reptiles live in forests.

            As India’s population grows rapidly, forests are disappearing and reptiles face the danger of being wiped out. Highways that cut through forests are deadly for these hapless animals. Many meet their end under wheels of vehicles as they try to cross these roads. Although many snakes eat rats and thus help farmers, all snakes mistakenly believed to be dangerous, and are killed in every encounter. Crocodiles are also killed for the same reason. Many species of turtles were used as food and medicine.

            However, there is improvement in these matters today, thanks to the efforts of wildlife officers, and the rising publicity about the threatened status of these turtles. The illegal pet trade is another threat to turtles.

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