Category Zoology

          Marsupials are mammals that do not give birth to fully developed young. Instead, the young are born at a very early stage, and then continue to develop while clinging to their mother’s body.

          When the young marsupial is born, it is tiny, blind and hairless. Its limbs are not even properly formed, but somehow it still manages to crawl through its mother’s fur to find its mothers’ nipples. Many marsupials, including kangaroos and wombats, have large pouches of skin around their nipples. A kangaroo’s pouch is deep and forward-facing, so that the young kangaroo does not fall out. Wombats are burrowing animals, so they have backward-facing pouches to stop soil getting inside. Other marsupials hardly have any pouch at all. Their young simply hang on to the nipples until they are old enough to let go.

          If a female marsupial has only one or two young, she can carry them in her pouch or, like the koala, on her back. Small marsupials, such as possums or bandicoots, which have several young at a time, must transfer them to a nest when they become too heavy to carry around.

          Most (but not all) marsupials live only in Australia. For millions of years, until the arrival of humans, Australia was isolated from the rest of the world. On the other continents, marsupials tended to lose out in competition for food with the placental mammals (those mammals that are born fully developed) and so, with the exception of the opossum family in the Americas, they died out. In Australia, they had no other mammalian rivals and so they thrived.

        Edentates are a group of mammals made up of anteaters, armadillos and sloths. The word “edentate” means “without teeth”, but only the anteaters have no teeth at all. Armadillos and sloths have a few very simple, grinding teeth.

          Sloths live in the rainforest of South America. They spend nearly all their time hanging upside down in the trees, feeding on leaves. Sloths move so slowly that they may only travel a few metres every day. In wet weather, a layer of green algae grows on their fur, which helps to camouflage them among the trees.

          Armadillos do not need camouflage they have a suit of armour to protect themselves. Made of bony plates, it covers the whole body, including the tail, head and limbs. Only the belly is soft, and some kinds of armadillo can protect even this part by curling themselves up into a ball.

          Anteaters feed on both ants and termites, which they detect using their keen sense of smell. The tongue of the giant anteater can unfurl an amazing 60.

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          When the first mammals appeared, all the continents were locked together in one large landmass. Over millions of years, they gradually drifted apart. This meant that the mammals were split up on to large “islands”, where they evolved into many different groups.

          North and South America eventually drifted back together again, and mammals from the two continents found themselves competing for food and territory with unfamiliar “relatives”. They also faced new predators. Some kinds died out altogether. The marsupials suffered in most parts of the world, but in Australasia, which was still isolated, many were able to thrive.

          Around the world, each kind of mammal adapted to its environment. Giraffes evolved a very long neck to browse from the tallest trees which other mammals could not reach. Whales and dolphins lost the fur and four legs of their ancestors and developed tails and fins to move more easily through the water.

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          Since the beginnings of life on Earth, all animal have gradually changed. Some have developed (or “lost”) legs, while others have grown horns, beaks or wings. Some kinds have died out altogether, giving way to others that are better suited to their environment. This process of change and adaptation is called evolution.

          Mammals are descended from mammal-like reptiles called pelycosaurs that lived on Earth about 300 million years ago. The first warm-blooded animals were probably the cynodonts. Small, fast-moving carnivores, the cynodonts may have had fur rather than scales. Fur is an essential feature of warm-blooded animals, as it helps them to keep their bodies at a stable temperature.

          The first true mammals evolved about 210 million years ago, when the dinosaurs dominated the Earth. In order to avoid the dinosaurs, the mammals came out only at night. Gradually, the three main groups of mammals evolved: marsupials, monotremes and placental mammals. The extinction of the dinosaurs meant that there was suddenly an absence of any large animals on land. This gave the mammals the opportunity they needed to spread rapidly and evolve into many different species.

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          Mammals are the group of animals to which humans belong. They are vertebrates (animals with a backbone) that give birth to live young and then feed them with milk. Most mammals have four limbs and a covering of hair or fur. Sea mammals, such as whales, have adapted to life in the water by losing their hair and hind limbs and forming their front limbs into flippers.

          All mammals are warm-blooded, which means that their bodies can control their own temperature. They obtain warmth from the process of burning fuel (food) inside the body, rather than from basking in the sun as the cold-blooded reptiles do. The skin and hair of the body are very important both for keeping in warmth in cold conditions and letting it escape to cool off the body in hot conditions. Most mammals also produce sweat, which cools the skin as it evaporates.

          Mammals have large brains and complex sensory and circulatory systems. They rely on their sense of smell more than any other kind of animal. Scent is used to communicate between members of the same species, to mark the borders of a territory, to find food and to detect an approaching predator.

          The most important feature which sets mammals apart from other animals is the way they care for their young after birth. All female mammals have mammary glands which produce milk after their young are born. The young feed on this milk, which gives them all the nutrition they need, until they are able to survive and feed on their own. By not having to find their own food, they can put all the energy gained from feeding into growing larger and stronger.

          During the period of suckling (feeding on milk), and also while the young learn to feed for themselves, the mother will protect them as much as possible from predators.

          Some female mammals raise their young alone while others share the task with the father or other members of a group.

          Most mammalian young, apart from the monotremes, are born live (not inside an egg). Small mammals can give birth to several young at one time, which grow and become independent quite quickly. The young of large mammals take longer to grow to full size, and need more care, so litter size (the number of young born at once) is smaller, often only one at a time.

          All mammals except the marsupials and the monotremes are born fully formed, though some, such as rabbits, are hairless, blind and helpless. They can grow further while in the safety of their burrow or den.

          In contrast, animals that live in open spaces, such as horses, cattle or deer, are able to walk and even run a few minutes after birth. If a predator appeared, they would need to run away with the rest of the herd.

          Many mammals live in social groups that can be made up of a few or many animals. Often the whole group will help to rear and protect the young. Carnivores such as lions or hyenas also hunt together, using their combined strength and skill to kill larger animals than they could tackle alone. Herbivores, such as deer or cattle, form large herds that give them some protection against predators.

          Like marsupials, monotremes give birth to under-developed young. However, monotremes young are born inside soft-shelled eggs. These hatch after a few days, and the young are suckled until they have developed fully.

          There are two kinds of monotremes: the echidna and the platypus. Both are found only in Australia and surrounding islands. Echidnas have a small pouch that holds their young after hatching. Platypuses do not have a pouch, but instead leave their young in a special burrow.

          Apart from a few types of shrew, monotremes are the only venomous mammals. Echidnas cannot use their venom but the platypus can kill a dog with poison ejected from a sharp spur on its leg.

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          Many birds have beautiful colours or feather displays. In many species, it is the males that are brightly coloured, to attract females. Females are duller in colour, for camouflage while nesting. Camouflage is also used by both sexes of some birds to avoid predators, or to hunt more effectively.

          Bee-eaters and kingfishers are small birds, often with jewel-like colours. As their name suggests, bee-eaters feed on bees, wasps and other insects. Before swallowing their prey, they crush the sting by smashing it on a branch. Kingfishers sit on branches over stretches of water, diving in to catch small fish in their beaks.

          The long-legged storks and herons also feed on fish, though some large storks are carrion-eaters. Most storks and herons are wading birds, standing in the shallows and snapping up fish in their long beaks. Their relatives, the flamingos, get their pink colour from the tiny plant and animal material in the water on which they feed.

          Hummingbirds and swifts are excellent flyers. They are small birds with long, pointed wings. Swifts can mate, feed on flying insects, and even sleep on the wing.

          Many members of the cuckoo family lay their eggs in the nest of a different species. After hatching, young cuckoos often kill their “true” nest mates. The hoatzin is probably related to the cuckoos. It nests over Rainforest Rivers. If attacked, the young drop into the water, then climb back up to the nest using sharp claws on their wings.

          With over 5000 species, the perching birds are the largest group of birds. They range in size from the tiny blue tit or wren to the large raven. They are land-living birds, with four unwebbed toes, three pointing forward and one backward. Most feed on seeds or insects, but some eat fruit or nectar. Many small perching birds fly in a bounding motion to save energy, flapping and closing their wings alternately.

          Most perching birds also belong to a sub-group called the songbirds. Though other birds can make short, simple calls, songbirds have extra muscles in their voice-boxes, allowing them to produce complex patterns of notes. Songs are used by males to establish territories and warn off intruders, as well as to attract females. Each species may have a large number of song variations, with birds from different areas having their own “accents”. Young songbirds learn songs from their parents and other adults.

          Most perching birds construct nests in trees or hedges, where their young will be safe from predators. The young are born naked, blind and helpless. They need to be kept warm and fed by their parents until they are old enough to fledge (leave the nest). Other birds such as ducks, gulls or game-birds, that lay their eggs in more exposed places, hatch out as fully-feathered young that can feed themselves almost straight away.

          Many songbirds, like other groups of birds, migrate to warmer places in the winter when food becomes scarce. They feed heavily before migration, laying down stores of fat for fuel on their long journeys. They return in the spring to breed, when there is a plentiful supply of food for themselves and their young.

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          Over millions of years, the ability to fly has enabled birds to escape from predators, and therefore to increase in number and variety. Every kind of bird has also adapted to survive in a particular habitat. In any one group of birds there may be several different families, all looking quite different from each other.

          The ratites include the ostrich, rhea, emu, cassowary and kiwi. They are all birds that have lost the ability to fly, because of a lack of natural predators, or because they have developed another means of defence. Some ratites are tall, long-necked birds that live in wide open spaces. They use their good eyesight to spot predators, and their long strong legs to run away at top speed. Ostriches can reach 65 kilometres per hour.

          Kiwis are much smaller birds, with hair-like feathers. They live in thick undergrowth, using their excellent senses of smell and hearing to detect predators, and their sharp claws for defence.

        Penguins are also flightless birds. Most live on cold, southern coastlines, such as Antarctica. Clumsy on land, in the water penguins are graceful and fast. Their stiff, flipper-like wings pull them through the water in pursuit of fish and squid. They breed in large colonies on land or on ice.

        Waterfowl (ducks, geese and swans) also feed in the water, as do grebes and divers, though these are mostly freshwater birds. They swim along the surface with their feet, which are often webbed. Their feathers are coated with a waterproof substance that traps air and keeps the birds afloat. Ducks tip upside down to feed, while grebes and divers plunge completely underwater. These birds feed on fish, invertebrates and plants.

          Birds of prey include eagles, falcons, hawks and vultures. They are all meat-eating birds, with sharp, hooked beaks and strong talons. They swoop down through the air, often at very high speeds, on to their prey – small mammals, birds, reptiles, insects or fish. Most birds of prey, especially the vultures, also eat carrion. Birds of prey have excellent long-distance vision, and can spot potential prey from several kilometres away.

          Though they are also hunting birds with strong beaks and talons, owls are a completely separate group to the birds of prey. Owls have flat faces with forward-facing eyes. Many kinds hunt in dim light or darkness. Their disc-like faces “collect” sound and direct it towards the ears, giving them exceptional hearing to locate their prey. Their feathers are soft, allowing them to fly almost completely silently, taking their prey by surprise.

          Seabirds spend much of their time in or near the water, feeding on fish or squid. Some kinds, such as cormorants or gannets, dive into the water from the air, or from high rocks. Albatrosses skim over the surface, scooping up food. Many seabirds gather together in colonies on cliffs to lay their eggs. Albatrosses and petrels only come on to land to breed. The rest of their lives are spent gliding on currents of air.

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