gq: Bird migration routes have been studied by a variety of techniques including the oldest, marking. Swans have been marked with a nick on the beak since about 1560 in England. Scientific ringing was pioneered by Hans Christian Cornelius Mortensen in 1899. Other techniques include radar and satellite tracking.
Question: What is the oldest way to study migration? Question: How have swans been marked? Question: Since when have swans been marked? Question: Who was scientific ringing pioneered by? Question: What are other forms of studying migration?