A twitcher is an enthusiastic bird-watcher. [British, informal]

What is a twitcher in UK?

Bird-watcher. The term twitcher, sometimes misapplied as a synonym for birder, is reserved for those who travel long distances to see a rare bird that would then be ticked, or counted on a list. The term originated in the 1950s, when it was used for the nervous behaviour of Howard Medhurst, a British birdwatcher.

What is the difference between birder and twitcher?

So, what is the difference between a birder and a twitcher? The birder is a passive birdwatcher who takes their time when birdwatching and enjoys whatever bird comes their way, while the twitcher is more active in their birdwatching approach, wasting no time, and seeks a specific kind of bird.