Category Science

          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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          The ancestors of birds were clearly reptiles – birds still have scaly legs, and they lay hard-shelled eggs. In fact, it is now known that birds are actually the living descendants of the dinosaurs.

          Like the dinosaurs, early birds had teeth, fingers and a long, bony tail, but they also had small wings and a few feathers. They may have used their wings to glide from tree to tree, or to give them extra speed when escaping from predators on the ground. Gradually, their body structures developed so that they could lift themselves into the air and fly.

          Archaeopteryx emerged in the late Jurassic Period, about 150 million years ago. Following Archaeopteryx came small flying birds such as Sinornis, which had shorter, more bird-like tails than Archaeopteryx. Up until the end of the Cretaceous Period, 65 million years ago, most birds still had teeth. These were useful for feeding on fish and insects, their main prey. Ichthyornis and Hesperornis were among the first marine birds and fed on fish, swooping over the waves like gulls or diving from rocks.

          At the end of the Cretaceous Period, the dinosaurs, along with many other reptiles died out, but many birds and mammals survived. A wide variety of different kinds of birds appeared, and by Eocene times, 50 million years ago, all the bird groups we know today had emerged.

          After the dinosaurs died out, some birds became large predators. Some kinds stood almost three metres tall. They were flightless, their small wings acting only to balance their heavy bodies. Ferocious meat-eaters, such as Andalgalornis and Diatryma, probably crushed mammals such as small, early horses in their powerful jaws. Other birds, such as Argentavis, a vulture with a seven-metre wingspan, were scavengers.

          Some kinds of birds have become extinct quite recently, due to the arrival of humans into their habitats. They were hunted for food, or preyed upon by rats, cats and dogs which the humans brought with them. Two groups of large, flightless birds, the elephant birds of Madagascar and the moas of New Zealand, were completely wiped out within just a few hundred years.

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            There are almost 9000 species of birds in the world today. Birds are warm-blooded, vertebrate animals with four limbs, two of which are adapted into wings. They have a toothless beak and a covering of feathers over their bodies and heads (apart from the bald-headed vultures). The feathers close to the skin are soft and fluffy for warmth, while long, stiff outer feathers help birds to gain height, steer and control speed when flying. Birds have light, hollow bones to reduce their weight in the air.

          Birds lay hard-shelled eggs, usually several at a time. After mating, the male and female often work together to build a nest ready to receive the eggs. Nests can be cup-like structures made of mud, grass and twigs, holes in trees, or even burrows underground. One parent usually sits on the eggs to keep them warm, while the other collects food. After hatching, most birds feed and protect their young until they are old enough to leave the nest.

          Because of their ability to fly at speed for long distances, some kinds of birds are able to migrate to warmer climates as winter approaches. They return to their breeding areas in spring, as food becomes plentiful.

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          Lizards are mostly quite small, quick-moving reptiles. They have a thick, scaly, and usually smooth skin. Most lizards have four legs and a tail, though some kinds are legless. They have long tongues that they flick in and out to “taste” the air or ground, to pick up information about their surroundings. Geckos also use their tongues to clean their permanently closed, transparent eyelids, while chameleons shoot theirs out to catch insects.

          Lizards have a special receptor on their heads that is sensitive to light. This is connected to the brain, and may act as a “third eye”, giving the lizard information about the patterns of day and night.

          Lizards are mostly land-dwellers, living all over the world except in Polar Regions. Some are burrowing animals, while many live in trees. Chameleons and some iguanas have prehensile tails to help them climb. Geckos have tiny ridges on their toes and can even walk upside down. Some lizards, such as skinks, are good swimmers, and will dive into the water to escape from predators.

          Almost all lizards are meat-eaters, feeding on insects, birds, small mammals and other reptiles. The largest lizard, the Komodo dragon, can reach three metres in length. It is a powerful predator, and can kill large mammals such as cattle. It has even been known to attack and kill humans.

          Lizards lay their eggs in warm, damp holes. Most female lizards take no interest in their eggs after laying them, but a few kinds guard the eggs until they hatch.

          The smaller lizards have many predators. They defend themselves with camouflage, or by running away, climbing trees or even playing dead. Several species are able to break off their own tails, to confuse an attacker while they run away. The tail has a special “weak point” that can be snapped without harming the lizard. A new tail will grow in its place.

          Snakes are a group of reptiles that have long, narrow bodies and tails, and no limbs. Their ancestors, however, were four-legged, lizard-like creatures. Some snakes have two tiny lumps on their bodies – the remains of the hind legs of these ancestors. Snakes have no eyelids. Instead, their eyes have a permanent, transparent covering.

          Snakes have many more bones in their spines than other animals. They move by flexing their belly muscles, which are attached to their many ribs. As they move, most snakes curve their bodies into a series of S-shapes, giving them greater speed.

          Most snakes lay eggs, and a few kinds will guard them from predators until they hatch. There are some snakes, such as sea snakes that give birth to live young. Young snakes are left to survive on their own.

          All snakes are carnivores. Some kinds eat small animals such as snails or worms, but many feed on large prey such as frogs, birds and mammals. Snakes have special loosely hinged jaws that can open extremely wide to take large prey. Their skin can also stretch. They swallow their prey whole, using their sharp teeth to pull it into the throat, and their muscles to squeeze it into the stomach. A snake may need to hunt and feed only every few weeks or even months.

          Some snakes have good vision, but most rely on special senses to hunt their prey. Like lizards, snakes are able to collect “tastes” from the air or ground by flicking out their forked tongues. Some kinds of snakes also have heat sensors on their heads that help them to locate live prey accurately, even at night.

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          The main characteristic that sets turtles and tortoises apart from other reptiles is their shell. It is made of bone fused to the skeleton, and covers both the back and belly. For extra protection, the shell is covered with thick, horny scales. If threatened, most turtles and tortoises are able to draw their heads and necks backwards into their shells.

          Turtles and tortoises do not have teeth. Instead they have a sharp, horny, beak-like mouth. They are mostly plant-eaters, but some kinds also feed on insects, fish, snails and even small mammals and birds.

         Tortoises are found on land. They have stumpy, scaly legs with short toes. Tortoises move slowly, relying on their high-domed, heavy shells to protect them from predator. Turtles live in the water, some in the oceans and others in freshwater rivers and ponds. Most have webbed feet, but some ocean turtles spend so much time in the water that they have developed paddle-like flippers that allow them to swim at speed.

         All turtles and tortoises breed and lay eggs on land. Some large sea turtles can lay over 100 eggs at once, returning to the same beaches every year. They dig holes in the sand, lay their eggs and then cover them over. Then they return to the water. After hatching, the young must dig their way to the surface. Many newly-hatched turtles are killed by predators as they make their way from the beach to the sea.

          Crocodilians are meat-eating reptiles that spend much of their time in water. They include crocodiles and alligators, and also the gharial, which has a long, narrow snout. Crocodilians use their long tails to swim, but can also run at speed on land. Most species live in freshwater rivers and lakes, especially tropical swamps. A few, such as the saltwater crocodile, live in sea estuaries.

          Crocodilians feed on a wide range of prey, including fish, turtles, birds, and mammals. The largest crocodiles, which can grow to more than seven metres long, will even kill deer and cattle. They lie in the water, waiting for their prey to come down to the water to drink. Then they lunge out with their powerful jaws, dragging their prey into the water to drown.

          Crocodilians can lie with their bodies almost completely hidden underwater, because their eyes and nostrils are on top of their heads. They also have a transparent “third eyelid” which closes to protect their eyes when they submerge. They can close off part of their throat to avoid swallowing water while feeding.

          Like all reptiles, crocodiles and alligators lay their eggs on land. Some kinds, such as the Nile crocodile, dig holes into which they lay their eggs, covering them over with soil to keep them warm. Others build nests of plant material. They will guard their eggs and defend their young.

          The tuatara is the only member of an ancient group of reptiles that lived on Earth even before the dinosaurs. Lizard-like in shape, the tuatara lives in burrows on small islands off New Zealand. It basks in the sun during the day, and feeds at night, hunting insects, worms and small lizards.

          Like turtles and tortoises, the tuatara is very long-lived. It becomes an adult at 20 years old, and may live for over 120 years.

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          Reptiles are cold-blooded, vertebrate animals that have a dry, scaly skin. The skin is made of one continuous sheet, rather than individual scales as in fish. Water cannot pass out through their skin, unlike that of amphibians. This means that reptiles do not need to keep their skin moist. Reptiles moult regularly, shedding their skin when a new one has grown underneath.

          Because they are cold-blooded animals, reptiles need to bask in the sun to raise their body temperature before they are able to move about in search of food. However, they do not need to eat as much food as the warm-blooded birds and mammals, so are able to survive more easily in harsh desert environments. Most reptiles lay eggs, either soft and leathery, or hard-shelled. Some give birth to live young. Reptiles do not care for their young after hatching or birth.

          Reptiles are descended from the early amphibians. The first reptiles were probably small, lizard-like creatures. Unlike the amphibians, they did not have to stay close to water to keep moist and lay their eggs. They were able to live more easily on land. The lizards, turtles and tortoises and the crocodilians (crocodiles and alligators), appeared during the Triassic Period, about 250 million years ago. Snakes evolved later, about 135 million years ago. Some modern-day reptiles have hardly changed since the time of the dinosaurs.

THE AGE OF DINOSAURS

          The period from 250 million to 65 million years ago is known as the Mesozoic Era. During this time, a new group of reptiles, the dinosaurs, emerged. They held their legs straight beneath their bodies, rather than sprawling out to the sides like other reptiles.

          For about 150 million years the dinosaurs were the only large land animals. They ranged in size from the chicken-sized Compsognathus to the 14-metre-tall Brachiosaurus. Some were slow, four-legged plant-eaters, while others ran swiftly on two legs. A few kinds were terrifying predators. Many of the plant-eaters lived in herds like modern-day cattle or horses, while the smaller predators hunted in packs, as hyenas and wild dogs do today.

          The dinosaurs all died out quite suddenly, but no-one knows why. Perhaps a huge asteroid hit the Earth, and a dust cloud plunged the Earth into cold darkness.

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