Category The Natural World

Although frogs and toads can live on land, they have to return to the water to breed. Common frogs can be found in many freshwater habitats. They often show up in garden ponds but are just as happy in lakes, canals and pools. Toads usually prefer wooded ponds and lakes and can sometimes be seen in boggy pools.

Frogs and toads are amphibians, which mean they are equally at home on land and water. Toads, however, generally spend more time away from water than most frogs. Their skin is leathery and watery and they do not lose water so easily on dry land. On land a frog hops to escape danger, whereas a toad will walk. The bodies of some frogs and toads have adapted to survive in very dry conditions, such as in deserts.

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According to the theory of evolution, some animal species become extinct because they are less successful than other species that gradually replace them.

These so-called ‘failed’ animals are also unable to adapt to changing circumstances. Humans have speeded up their extinction by changing the environment so rapidly that animals do not have the time to adapt. For example, the destruction of Indonesian rainforests has left nowhere for the orang-utan to live. It would take millions of years for the animal to evolve into a ground-living creature. Hunting is the main reason for the reduced numbers and probable extinction of animals such as the tiger, the blue whale, and the giant panda.

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Young swans, or cygnets, are hatched with a complete covering of down and can take to the water as soon as they leave the nest, within 24 to 48 hours. Right from the beginning they can forage for themselves, but at least one parent remains with them, guarding, guiding and, initially, brooding them at night. The dark downy plumage is retained for two to six weeks and it then replaced gradually by the juvenile feathers. The flight feathers are the last to develop, taking from five weeks to as many months. By the age of six months the cygnets are practically indistinguishable from adults in plumage and in size.

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Migration is the mass movement of groups of animals or birds. It is caused by the need to find food, by climatic changes during the year, and by the need to breed. Every autumn, for example, swallows gather in large flocks to rest before they begin their long migration to Africa. Swallows, and their relatives, swifts and martins, all migrate to Africa when the weather becomes too cold for them to catch their insect prey. They return in the spring when the weather in northern Europe begins to warm up. The Arctic tern makes the longest-known migration of any bird we know, by travelling from the Arctic to the Antarctic and then back again. On its flight it passes through Japan, Alaska, Canada and Fiji before returning home again to breed.

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An animal is classed as a vertebrate when it has a backbone to provide support for the muscles and protection for the spinal cord. Vertebrates include fish, amphibians, reptiles, birds and mammals. The backbone is actually a series of small bones called vertebrate. They are joined together and locked with rope-like ligaments to provide a flexible but extremely strong anchor for the back muscles. The spinal cord runs down a channel inside the vertebrate, providing protection from damage. Some primitive fish, such as sharks and rays, have a spine made of a rough rubbery material called cartilage. There are approximately 45,000 living species of vertebrates. In size, they range from minute fishes to elephants and whales (of up to 100 tons), the largest animals ever to have existed. They are adapted to life underground, on the surface, and in the air.

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Carl Linnaeus (1707-1778) was a Swedish botanist and explorer who was the first to create a uniform system for naming plants and animals. Most plants and animals have popular names that vary from place to place. Scientific names are given so that the same name is recognized everywhere. Latin is the language used for scientific names. The scientific names are in two parts. The first is the generic name, which describes a group of related living things, and the second name is the specific name, which applies only to that living thing.

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Upon his return from the voyage, Darwin turned over all the specimens he had brought back to cataloguing experts in Cambridge and London. In South America he had found fossils of extinct armadillos that were similar but not identical to the living animals he had seen. On November 24, 1859 Darwin published his theories in a book called The Origin of the Species. It caused a great sensation, but it was some time before it was accepted by the scientific world. The first edition sold out immediately and by 1872 the work had run through six editions. It became generally accepted that evolution took place along the lines that Darwin suggested. His theory on evolution of species solved many puzzles.

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In the year 1831 Charles Darwin (1809-1882) set out on an exploratory voyage in the ship Beagle, heading for South America. The voyage lasted five years and during this time Darwin kept careful notes of everything he saw, in particular the strange animal life on the Galapagos Islands, off the western coast of Ecuador. He was disturbed by the fact that the birds and tortoises of the Galapagos Islands tended to resemble species found on the nearby continent, while inhabits of similar adjoining islands to the Galapagos had quite different animal populations. In London Darwin later learned that the finches he had brought back belonged to a different species, not merely different varieties, as he had originally believed.

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