Read the Passage

A Long Flight South As autumn days grow shorter, many monarch butterflies begin a remarkable trip. Monarchs from parts of the United States and Canada travel south to mountain forests in central Mexico. Some may cover about 2,000 miles before reaching their winter home. The butterflies gather in clusters on the branches of oyamel fir trees. The forest is cool enough for them to rest, but not as harsh as the northern winter. When spring arrives, the monarchs head north again. They lay eggs along the way, and new generations continue the journey. It can take several generations for monarchs to spread back across their northern range. How do the butterflies find their way? Scientists think monarchs use clues from the sun and an internal sense of direction. Their journey is especially surprising because the butterflies making the trip south have not visited the Mexican forest before. Each year, their seasonal travel helps them find places with conditions suited to resting and raising the next generation.