Extinction

Some extinctions happened naturally. If there are long lasting changes to a habitat, animals and plants must change to meet and survive those changes (this is called adaptation), move to a similar habitat elsewhere or die.

Throughout history there have been cases of animals becoming extinct as the world changed, such as sabre-toothed cats and woolly mammoths.

Dinosaurs became extinct naturally. The most popular theory is that a huge meteor hit the earth when the dinosaurs were the dominant animals. There was volcanic activity, and a huge tsunami (tidal wave) so low lying areas were flooded and thick clouds of dust hung in the atmosphere for many years so the sun's rays could not reach the earth and it became very cold. The dinosaurs were too huge to shelter from the cold and had no way to get warm. Being reptiles, they depended on sunshine to warm them from the outside of their bodies. The changed weather meant the plants were affected, so herbivores could not eat the plants they usually ate. Carnivorous dinosaurs could feed on the herbivores for a while, but small animals were able to shelter and were hard to find. Because the dinosaurs could not adapt to their drastically changed environment, they died out. They became extinct.

In the last few centuries, however, the number of extinctions has speeded up to an incredible rate. It is humans who have made this a faster process, by killing animals, destroying habitats, polluting the atmosphere and causing the warming of the earth.

Animal behaviour is complicated, and sometimes humans affect the way a species is organised, and if the species cannot change their habits, they die out. Some examples of this:

There was a species of pigeon in North America & Canada called the Passenger pigeon. Flocks were huge, with millions of birds in a flock. They were easy to kill and apparently delicious to eat. Humans killed many, many millions. Then a law was made to ban hunting them because numbers were decreasing. However, even though there were still hundreds left, the pigeons still died out. It is thought that their breeding behaviour could only properly happen within a huge flock, and when flocks were down to a hundred or less, the pigeons did not know how to find a mate and a breeding place. They could not change their habits to adapt to being in small flocks. They became extinct in 1914.

Find out about Passenger pigeons, including the death of the last one: http://www.si.edu/Encyclopedia_SI/nmnh/passpig.htm

Go here for a drawing of male and female Passenger pigeons:
http://www.songbird.org/birds/extinct/passpigeon.htm

A deer called Schomburgk's deer, with spectacular antlers, was native to Thailand (then called Siam), and lived in swamps. They were hunted, but never in big enough quantities to cause extinction.

However, in the mid 19th century, the swamps were drained and the nearby forests were cut down for railways and farming. There was nowhere for the deer to go, and they gradually died out. The last one died in captivity in 1938.

When an animal becomes extinct, there is always an effect on other things. This is because of biodiversity, the linking of things in nature. An example of this:

The dodo (say dough dough) was a large flightless bird on the island of Mauritius. Sailors visiting the island hunted and ate dodos. Rats came onto the island from the ships. Introduced animals such as pigs and monkeys were brought onto the island. The dodo nested on the ground, so the eggs were easily eaten by the introduced animals. The dodo became extinct in 1681.

It was recently discovered that there are only 13 mature calvaria trees on Mauritius, and they are over 300 years old, and therefore nearly at the end of their lifespan. There were no younger trees of that species. When scientists tried to find the reason for this, they discovered that the seeds had had to pass through the digestive system of a dodo before they could germinate. Because this could not happen any more, it looked like that species of tree would also become extinct. Fortunately it was discovered that domestic turkeys could substitute for dodos, seeds were fed to the turkeys and germinated. There are now some seedlings and hope for that tree species.

Today, about one quarter of the world's mammals are in danger of becoming extinct in 30 years (many of them in Australia). And that's just mammals - there are also reptiles, birds, insects, fish and plants that are endangered. About half of Australia's native animals are endangered.

Today environments and habitats are changing more quickly than ever before because of human activity. In these modern times, more animal species have become extinct in a short period of time than ever before in the history of the planet.

It is estimated that by the year 2050, about 60,000 plant species and between 660,000 and 1,860,000 animal species will be extinct or threatened.

Some of the ways that humans have caused animal and plant species to become extinct or threatened:

Cutting down of vast areas of trees.

Monkeys and other primates sold illegally all around the world for their fur, to be kept as pets or for scientific research.

Exotic birds such as parrots and macaws, and many reptiles are popular pets. People smuggle them out of their native countries to sell them for huge sums of money. Many of these birds and reptiles die during the journey.

Big cats such as the leopard and jaguar killed for their fur.

Rivers polluted and overfished. Sometimes the pollution has poisoned the water so that fish, animals and humans have become sick and died.

Fishing boats in the sea drag huge nets that scoop up thousands of fish and other animals. They keep the fish they want, and dump thousands of unwanted dead fish, dolphins and turtles overboard.

If you use any part of this in your work, acknowledge this source in your bibliography like this:
Sydenham, S. & Thomas, R. Extinction [Online] www.kidcyber.com.au [2003]