More than 5 billion birds migrate across the Northern Hemisphere each year. Of Wisconsinâs 235 breeding species, 133 are neotropical migrants, meaning they winter in Central and South America. The common tern has the longest fall migration, traveling as far as 16,000 miles! Most birds migrate at night when it is cooler and there are fewer predators. During migration, they need safe places along the wayâsuch as parks and natural areasâ to land, feed and rest.