การฟัง TOEFL

🎧 บทถอดเสียง

Listen to part of a lecture in a biology class. The professor is discussing the migration patterns of monarch butterflies. 'Okay, so we've talked about how monarch butterflies migrate thousands of miles each year to overwintering sites in Mexico. But what's really fascinating is that the butterflies that make the journey are not the same ones that started the migration. Actually, it takes several generations to complete the round trip. The butterflies that leave the northern United States in the fall are the great-great-grandchildren of those that left Mexico in the spring. They somehow find the same trees, even though they've never been there before. Scientists have studied this for decades, and recent research suggests that their internal compass, which is based on the sun's position, is calibrated by an internal clock in their antennae. But there's also evidence that they use the Earth's magnetic field as a backup, especially when the sun is obscured by clouds. This dual navigation system is remarkable, but it's also fragile. Climate change and habitat loss are disrupting their journey, and that's a major concern for conservationists.'