This week bird-watchers thronged to a sewage-treatment plant near Melbourne in order to get a look at a monochrome duck. One of them counted “35 cars of birders”, adding: “It was a mega-twitch.”

A “twitch” here is what “twitchers” engage in: the pursuit of a previously located rare bird. But why this term? It might be plausible to relate it to the sense of “to twitch” meaning to pluck or snatch, or the twitching of bushes and twigs by ill-concealed watchers, but a letter to British Birds magazine in 1983 is the canonical source.

There, one Bob Emmett explained how, in the 1950s, he would give his friend Howard Medhurst a ride on the back of his motorcycle when their gang went off to spot birds. At the destination Medhurst would “totter off the back” and “shiveringly light up a cigarette”. Since everyone was excited, the others began to imitate his jerky movements, and travelling to see a rare bird became “to go on a twitch”.

Some serious “birders” think twitchers are just sensationalist box-tickers, but happily there is room enough in the world for both styles of avian admiration.