The days are growing shorter and colder, and birds, butterflies, and other animals are starting to head to warmer climates for the winter. These journeys are often thousand of miles—monarch butterflies can fly as far as 3,000 miles to winter in Mexico. On today’s Please Explain, we’ll find out how these animals know when and where to go. We’ll also talk about how climate change is affecting animal migration. We’re joined by Leon Kreitzman, co-author with Russell Foster of Rhythms of Life and Seasons of Life; and Dr. David Wilcove, Professor of Ecology and Evolutionary Biology and Public Affairs, Woodrow Wilson School, and Director of the Program in Environmental Studies, at Princeton University, and author of No Way Home: The Decline of the World's Great Animal Migrations.