DK Science: Animals Growing Up
As animals grow they can change in both their form and their behaviour. Some animals change suddenly and drastically ? for instance, caterpillars metamorphose into butterflies in a matter of weeks. Most animals develop gradually. Some young animals are cared for by parents. This allows them to learn about life from an experienced adult. Others are left to fend for themselves and have to rely on their instinct.
The babies of pouched mammals are born very small and undeveloped and then grow in their mother?s pouch. They gain all the nourishment they need from their mother?s milk. A baby red kangaroo does not leave the pouch for 190 days and will stay with its mother for at least a year afterwards.
In many animals, parental care simply means protection. The young are safe as long as they remain close to their guardian. Female cichlid fish have a pouch in their throats to carry their eggs. When the eggs hatch, the young fish remain in the mother?s mouth until they can fend for themselves.
Animals with exoskeletons can only grow by moulting (shedding) their outer skin. Woodlice are unusual because, unlike other crustaceans, they shed half their shell at a time. The exoskeleton breaks in the middle and the back half is shed first. A few days later the front half breaks off. During moulting, the lice are at risk and often hide away from predators.
All female wildebeest have calves over the same two weeks to reduce the number of opportunities that predators have to attack their young. The calves can stand and run 20 minutes after birth ? an essential adaptation for their survival. They also follow the first moving thing that they see ? often their mother ? in a process called imprinting. It is a form of learning that ensures the calves stick close by their mothers as they move around and graze.
All baby birds need parental care to survive. Some types of bird are naked, blind, and completely helpless when they are born. Others are covered in down feathers, have fully developed eyes, and are able to walk about within a few hours. Blue tit chicks are helpless when they are born so they huddle together for warmth while the parents hunt for food. They open their beaks when one of the adults returns, stimulating the parent?s instinct to feed them.
Some babies are left to fend for themselves from the start. The female loggerhead turtle buries her eggs in the sand and then abandons them. When the young turtles hatch, they dig their way to the surface and instinctively head for the sea. Many of the hatchlings are eaten by birds and other predators as they make their way over the sand.
Elephants live in close-knit family groups. From the moment a calf is born, it has the benefit of its mother?s guidance and is protected by all the females in the group. Elephants live up to 60 years and mature slowly. Calves stay with their mothers for several years to learn all they need to know to survive, such as where all the water holes are.