Birds really do flock together. The trajectories of annual avian migrations converge as birds seek to pass over mountains, oceans, and other geographical features that can constrain their flight paths, according to a new study from the Cornell Lab of Ornithology.

Their research, published in the journal Proceedings of the Royal Society B, examines 118 migratory birds in the Western Hemisphere, showing that as species of birds cross the Gulf of Mexico, the isthmus of Panama, and other specific areas, their flight paths converge along the most efficient routes. When flying above the isthmus, for instance, birds want to stay above land for as long as possible, so there's only so much space in which they can fly. Over the ocean, birds can’t stop to rest, so they need to fly where wind patterns will be favorable to their travel plans. 

The GIF above, made by the Cornell scholars, shows the rhythm of annual bird migrations. These species, at least, move north for half a year, then begin to turn southward around August. Some venture as far as Patagonia, even though August marks the end of winter in the southern hemisphere. Many species, however, hang out in Central America for the cold months and head back north around April. 

To see which species is which, check out this key

Image courtesy Cornell Lab of Ornithology 

[h/t: We Are Wilderness]