Context: 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?
Answer: marking

Question: How have swans been marked?
Answer: a nick on the beak

Question: Since when have swans been marked?
Answer: 1560

Question: Who was scientific ringing pioneered by?
Answer: Hans Christian Cornelius Mortensen

Question: What are other forms of studying migration?
Answer: radar and satellite tracking