【新外研版】教材帮必修第一册 Unit 5 Understanding ideas
The Monarch's Journey
1 Many animals move from one place to another at certain times of the year.This annual movement is called migration.They migrate to find food,seek a partner,or in search of warmer weather.One of the most wonderful migrations in nature is that of the North American monarch butterfly.
2 Every autumn,millions of these beautiful insects with fine black and orange wings begin a long and difficult journey.Somehow they manage to travel around 4,000 kilometres south and find their way to California or Mexico.However,until recently no one knew how they did this.
3 A team of scientists led by Professor Eli Shlizerman at the University of Washington has now found the answer.They have found out that the monarch is able to tell the time of day.It uses its eyes to measure the position of the sun.These two pieces of information — the time of day and the point where the sun is in the sky — allow the butterfly to determine the way to go.Eventually,it manages to reach the places where it will spend the winter.
4 The solution to the mystery of the monarch's amazing ability comes at a time when it is in serious trouble.Its population has crashed by as much as 90 per cent in the last few years.Sadly, human activity is the main reason why the number of monarch butterflies is falling.In many of the places where the butterfly can be found,people are destroying the natural environment.They cut down trees and use chemicals that kill the plants that monarch caterpillars eat.
5 The research on the monarch's behaviour has however led to a greater awareness of this creature.People have been working together to record its migration and make sure that there are enough plants for it to feed on.If this works, there may come a time when the number of monarch butterflies increases once again.The more we know about this lovely creature,the greater the chance it will survive and keep its place in the natural world for a long time to come.