Millions of birds migrate each year from northern latitudes to the Indian subcontinent to escape freezing temperatures, traveling vast distances through mountain passes. They come in a great diversity of sizes and shapes, from small sparrows to large cranes. Some birds, like the Arctic tern, travel continuously between the Arctic and Antarctic circles each year, while others fly over 5,000 kilometers between Siberia/Alaska and Hawaii. Birds prepare carefully for these long flights, eating more food to store fat for fuel. They use the sun, stars, magnetic fields, and visual landmarks for navigation, and fly in flocks to help stay on course during migration.