twitcher
noun
1
a bird-watcher. Bird-watchers' slang. Originally from the observation that many bird-watchers do twitch with excitement and applied only to excitable members of the bird-watching community, now well known and applied generally UK, 1977.
2
anyone with a pedantic interest in, and an obsessive knowledge of, a specific topic. Extended from its sense in the bird-watching world UK, 2003