Every autumn, _(million) of North American monarch butterflies begin a long and difficult journey. Somehow they manage to travel around 4,000 kilometers south and findway to California or Mexico. However, until recently no one knew how they did this.
A team of scientists _(lead) 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 (eventual), it manages to reach the place it will spend the winter.
The solutionthe mystery of the monarch's amazing ability comes at a time when it is in serious trouble. Its population _(crash) by as mush as 90 per cent in the last few years. Sadly, human activity is the main reason the number of monarch butterflies is falling. In many of the places where the butterfly can be found, people are destroying the natural environment. The research on the monarch's behaviour has however led togreater awareness of this creature. People have been working together (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.
