HOW ANIMALS RAISE THEIR YOUNG

The newborn young of many species need no care from their parents. Even from birth, they can move about and find food on their own. The young of other species need parental care for some time after birth. One or both parents provide them with food and protection until they are old enough to manage for themselves.

Most kinds of animals never see their parents. For example, clams and many other invertebrates release their eggs and sperm into the water, where fertilization takes place. Carried around by ocean currents, the young of these animals may travel far from where their parents live. The female leatherback turtle swims thousands of miles or kilometers in the ocean to tropical beaches. She then digs a hole on the beach and lays her eggs. The eggs hatch in the warm sand after the female has returned to the sea.

Providing food is one of the main ways animals care for their young. Even females who never see their offspring provide them with food. The female's eggs contain yolk and other nourishing substances that serve as food for the developing embryos. Female sea urchins and herring produce vast numbers of small eggs, each of which has little yolk. Offspring from these eggs are extremely tiny when they hatch and must find their own food to grow. Their chance for survival is relatively small. Female birds, on the other hand, lay only a few eggs, each with large amounts of yolk. Offspring from these eggs are relatively large and have a higher chance of survival.

Some animals that do not see their offspring provide their young with food in addition to that in the egg. Many flies lay their eggs on rotting fruits, which supply the young flies with food. The female digger wasp lays her egg on a grasshopper that she has stung, paralyzed, and buried. After hatching, her offspring feeds on the grasshopper. The female dung beetle finds fresh dung (manure), rolls a piece into a ball, and then buries it. She lays her egg on the dung ball. After hatching, the young beetle feeds on the dung.

Mammals nurse their babies-that is, they feed them on the mother's milk. The nursing period lasts only a few weeks in mice, hares, and many other species. But among some larger mammals, such as elephants and rhinoceroses, the young may nurse several years before they are weaned-that is, taken off the mother's milk.

Incubation. In many species, the mother and sometimes the father remain with their eggs and young. Birds incubate their eggs by sitting on them in a nest. Incubation keeps the eggs warm and helps the embryo inside to develop quickly into a young bird. After the eggs hatch, the parents may make many hunting trips each day, trying to catch enough insects to feed the hungry nestlings (young birds). When the young are old enough to hunt, they leave the nest and fly away.

Among many species of birds, including pigeons and starlings, the parents take turns incubating the eggs. Among ducks, geese, and some other birds, the females are the only incubators. In most species of hornbills, the female even imprisons herself inside a walled-up nest chamber to incubate eggs. The male passes food to the female through a tiny slit in the wall. In a few species of birds, the male does all the incubating. For example, a female emperor penguin lays a single egg, which the male then incubates on top of his toes. He tucks his toes and the egg under the fluffy feathers of his belly. When the egg hatches, the little penguin stays warm and grows in this cozy "nest."

Female pythons also incubate their eggs. They produce the heat to warm their eggs by twitching their muscles, much as people do when shivering. After the baby pythons hatch, they must find food and shelter on their own.

Providing shelter. Some species provide shelter for their young. A female lizard may lay her eggs in an underground nest, where they are hidden from predators. The huge nests of sociable weavers, a type of African bird, protect the baby birds from bad weather and enemies. Some frogs and fish build nests for their eggs and young. A few tropical frogs carry their tadpoles around on their backs until they find a safe pool of water for the young frogs.

Parents sometimes provide shelter for their offspring within their own bodies. The male seahorse carries the female's eggs in a pouch. When the young seahorses hatch, the male releases them from the pouch. Female kangaroos, koalas, opossums, wallabies, and other marsupials give birth to tiny, poorly developed offspring. The babies mature in a pouch on the mother's abdomen. There, they nurse and are protected by the mother. One kind of Australian frog swallows her eggs into her stomach, where they develop. After the eggs hatch, the female opens her mouth, and tadpoles and small froglets come out.

Providing protection. Parents often protect their young from enemies. A male stickleback fish will attack any predatory fish or insect that approaches its young. A female scorpion carries her babies on her back and defends them with the poisonous sting on the tip of her long tail. Female crocodiles guard their nests and will fight any predator that comes near. As young crocodiles begin to hatch, they cry out, and the female helps them dig out of the nest. She then gently picks them up in her jaws and carries them to a nearby pond. A female bear will sometimes attack hikers who venture too close to her cubs. A female pet dog may attack even her owner if she fears that her puppies are threatened.

Group care. Some animals live together in groups of several families. As many as a hundred pairs of sociable weavers raise their chicks together in a large nest. Several female lions may care for their young cubs together. Naked mole rats live in underground colonies. One female produces offspring. Most of the other females help tend the young. Many monkeys and baboons live in small groups. All the adults in a group will work together to defend their young from an attacking leopard. When attacked by a wolf, a herd of musk oxen will protect their calves by placing them between adults.