An informalcompetition among birdwatchers to determine who can see or hear the largest number of species of birds within a single calendar year and within a specific geographical area.
2005, Sean Dooley, The Big Twitch, Sydney: Allen and Unwin, page 21:
And so the record stood. Nobody seemed to be much concerned with it, unlike in Britain or the States where Big Years are hotly contested amongst twitchers.
Used other than figuratively or idiomatically: seebig, year.
