Nehaveigur

Before migration was understood, people [in 19th century Europe] struggled to explain the sudden annual disappearance of birds like the white stork and barn swallow. Besides migration, some theories of the time held that they turned into other kinds of birds, mice, or hibernated underwater during the winter, and such theories were even propagated by zoologists of the time.

Birds that returned to Europe from Africa that had arrows stuck in them proved that the birds were migrating. Amazingly, the arrows did not diminish the birds’ ability to fly enough that they couldn’t cover thousands of kilometers between Africa and Europe. The Pfeilstorch (German for arrow stork) is the most famous example.

Thanks to by Telescopic Turnip for the pointer.