Hen migration routes are already researched by a number of methods including the oldest, marking. Swans happen to be marked which has a nick about the beak since about 1560 in England. Scientific ringing was pioneered by Hans Christian Cornelius Mortensen in 1899. Numerous massive birds (like eagles and vultures) https://ledbookmark.com/story6065073/the-best-side-of-why-petsky-store