44 L5-Greate Migrations

该页暂无翻译

Oxford Read and Discover level 5 Great Migrations by Rachel Bladon

Introduction Around the world, day and night, and in every season, animals are moving from one place to another. They move over land, in the air, or through water. Some make short journeys, others go across the world. These animals are all migrating. Animal migrations are amazing. What animals can you see below? Why do animals migrate? How do animals find their way when they migrate? What animal has made the longest migration? What animals migrate to or from your country? Discover! Now read and discover more about some great animal migrations!

Chapter 1 On the Move Migration is when animals move from one place to another. Sometimes huge numbers of animals migrate together, but some animals migrate thousands of kilometers all alone. Why Do Animals Migrate? Many places are not good for animals to live in all year long. The places are sometimes too cold or hot, or not good for baby animals. Sometimes there is not enough food. Animals have to move away for part of the year or for part of their lives. They migrate to find food, water, and a safe place to live or breed. Sometimes all the animals in a species migrate. This is called complete migration. If only some animals in a species migrate, it's called partial migration. Discover! Arctic terns migrate from the Arctic to the Antarctic and back every year. That's almost 50,000 kilometers! When To Go Animals that migrate are called migrants. Many migrants leave their home at the same time every year. They reach the end of their journey at about the same time, too. So how do they know when it is time to leave? Animals see things in the world around them that tell them to leave. The days get longer or shorter. The weather gets hotter or colder, or there is less food to eat. Scientists think that when migrants see that these things are changing, their bodies make special chemicals called hormones. The hormones make an animal eat lots of food so that it has enough energy for its journey.

Finding Their Way Animals are very good at finding their way. Some use landmarks— important places that they can see, for example, mountains and coasts. Others use the sun during the day, or the moon and stars at night. Some animals use smells to help them to find their way. Scientists think that some animals can even feel Earth's magnetic field and use it to tell them where they are. It's like the animals have a compass inside. Discover! Some animals, like bats and whales, make special sounds when they are moving. The echoes from these sounds help them to find their way. Dangers Migrating is often dangerous. The journey is very tiring for animals, and they sometimes find it difficult to get food and water. They are in danger from bad weather and predators— other animals that want to kill and eat them. There are many dangers, but these do not stop migrants. They have to make long journeys to find safe places to breed and a home with lots of food!

Chapter 2 Bird Migrations There are many different species of bird, and about half of them migrate. Some birds only travel a few kilometers, but others go all the way around the world! Where Do Birds Migrate? In the northern half of the world, days are long in summer, and birds can easily find food for their young. In winter, many of these birds fly south because it's too cold in the north and there is not enough food. Birds in the southern half of the world fly north for winter and back south for summer. Many birds also migrate between east and west, usually looking for warmer winter weather near the ocean. Most birds in the Tropics do not migrate because it's always warm there. Discover! Bar-tailed godwits from New Zealand fly further without stopping than any other bird. They fly 11,500 kilometers to China. Then after feeding, they fly another 5,000 kilometers to Alaska to breed! Getting Ready Before birds migrate, they need to eat a lot of food so that they have enough energy for their journey. Some birds double their weight before migrating. Their muscles become stronger, too. Before migrating, many birds also molt they lose their old feathers and new ones grow. They wait for good weather, and then they are ready to go!