We all know birds in North America fly south for the winter and revisit us come spring, but have you ever wondered what their journey looks like once they leave our backyards?

Ornithologists from Cornell University developed this migration map to show a year’s worth of travels for more than a hundred bird species across the Western Hemisphere. Each dot represents a different avian group as it flies thousands of miles to breed and feast. To create the map, the researchers used data from more than a million observations made by amateur bird watchers through eBird, a citizen science project.

“This is the first comprehensive picture of where these birds are moving across the entire year,” said Frank La Sorte, an ornithologist at Cornell and one of the map creators. It would have cost millions of dollars to gather the information needed to reconstruct the trajectories with traditional tracking methods, he said. “Even if we tracked hundreds and hundreds of birds, we would not get this level of detail.”

Dr. La Sorte said that through their analysis, first published last week in a biological research journal, he and his colleagues attempted to address what they consider the “big question in migration ecology”: What migration strategies do birds use to journey across the Western Hemisphere?