By Elise Brosnan
In the 19th century, a curious phenomenon stumped European bird watchers and zoologists. Why did some species of birds disappear and then reappear every year? People back then had no way to track birds as they traveled long distances, so they had to come to their own conclusions.
One popular theory was that birds hibernated at the bottom of a pond or stream, the same strategy used by aquatic frogs and turtles. This claim was buoyed by fisherman, who said they were catching birds in their nets. In earlier times, other scientists, such as Aristotle, believed that birds metamorphized, transforminginto other bird species like caterpillars transform into butterflies. Other theories were even more bizarre. In 1703, a Harvard professor proposed that birds were flying to the moon!
In 1822, one White Stork helped put an end to this mystery. The bird landed near the German village of Klütz with a 30-inchspear through its neck. The spear was discovered to be made from African wood, meaning this stork must have traveled between the continents. Being a literal people, the Germans felt this strange, new animal needed a new name: Pfeilstorch, or arrow-stork. Amazingly, there have been 24 subsequentrecorded Pfeilstorchs—birds that have successfully migrated to Europe with an African spear embedded in their flesh.
The Pfeilstorch was the first concrete evidence for migration, the annual, large-scale movement of birds between their breeding and non-breeding territories. Migration may be less fantastical than space travel or shape-shifting, but it is no less impressive. Twenty-five recorded Pfeilstrorchs traveled 2,000 miles to Africa, got impaled, and then traveled 2,000 miles back. Their 4,000mile round trip pales in comparison to the Artic Tern, which makes an almost 60,000-mile voyage between the poles. The Common Swift has a shorter migration, traveling from itsbreeding grounds in Scandinavia to its feeding grounds in Sub-Saharan Africa. However, because of the recent development of lightweight accelerometers commonly used in smartphones, researchers have been able to prove that the Common Swift has the longest uninterrupted flight of any bird. Common Swifts eat, drink, mate, and even sleep while airborne, and consequently, some of them never set foot on the African continent they return to each year. By the time they touch back down in Scandinavia, these birds have been airborne for an entire 10 months.
Although we have had proof of migration for nearly 200 years, in many ways it still perplexes us. We still don’t have definitive answers to what triggers migration, how birds navigate across oceans, or why birds choose to go on these long and arduous journeys at all. With all of these unknowns, one thing is for certain: technological innovations like accelerometers, as well as random happenstance like the Pfeilstorch, will continue to shed light on one of the most beguiling mysteries of the natural world.