Twitchers' vocabulary is the set of jargon words used by twitchers. Twitchers are committed bird-watchers who travel long distances to see a new species to add a species their "lifelist", "year list" or other lists. Some terms may be specific to regional birding communities, and not all are used due to dialectic and cultural differences.
Some species have nicknames, for example: "RB Flicker" for red-breasted flycatcher, "Gropper" for grasshopper warbler, "PG Tips" for Pallas's grasshopper warbler; in the US, these are generally reserved for common species ("TV" for turkey vulture or "butterbutt" for yellow-rumped warbler). Twitchers (and birders in general) will also use a mixture of scientific and slang terms for feather tracts and so on.