Migration in Birds Draft 1/Week 5

In the old times, naturalists did not have a solid explanation on how birds migrated. Aristotle found out that cranes migrated seasonally. Based on discoveries and technology, we all know that land birds fly one place to another depending on the seasons. When migration season happens in North America, birds usually to move north to south direction. It is known that most migratory birds breed in the south and returns to the north. Birds living in the southern hemisphere will not migrate to the north as much as the northern birds travel. Some birds only travel during the day, others at night, or even both such as the waterfowl and shorebirds. Birds can fly as high as 2000-4000 meters and sometimes much higher and every bird has different altitude level that they can travel.