Twitchers are not shy of traveling long distances to add a new species to their personal or otherwise special list. In his book with the tile “The Wonder of Birds” Jim Robbins frequently addresses human-bird relationships and the human perception of the world of birds. He introduces the terms megatick, crippler and plastic as follows (page 250 in ):
The United Kingdom, though, seems to have more obsessed bird-watchers per capita than anywhere else in the world. It's home to the “twitchers,” a particularly fanatical group who make long journeys to see rare birds and presumably go into paroxysms of delight when they see one. They have their own lingo—a megatick is a very rare bird, a crippler an especially showy rare bird (perhaps because it causes people to stop in their tracks), and plastic refers to a bird that has escaped from captivity.
Twitchers' terms are typically shorter and easier to grasp and remember than scientific terms. Did they derive as slang words in the twitcher network of twitter-communicating birders? Tweets composed of twitchers' terms announcing bird sightings?
Keywords: twitching; grasping; jargon; lingo; slang; human-avian world.
References and more to explore Wikipedia: Twitchers' vocabulary. Link: en.wikipedia.org/wiki/Twitchers%27_vocabulary.
 Jim Robbins: The Wonder of Birds. Spiegel & Grau, New York, 2018.