A sea bird — slim, black and white, with long narrow pointed wings and a tail that splits into two points, like an open pair of scissors. That forked tail is the thing to look for. Terns are lighter and more elegant than gulls, and they fly differently: they hover over the water, then suddenly drop straight down to catch a fish.

Because they look a bit like small graceful gulls, people sometimes call them 'sea swallows' — the forked tail is why. Birdwatchers care a lot about telling the different kinds apart: common tern, little tern, Arctic tern. The Arctic tern is the famous one, because it flies from the Arctic to the Antarctic and back every year, the longest migration of any animal on earth.

The word is an ordinary countable noun: a tern, two terns. It is not a common word in daily conversation — you meet it in nature writing, on birdwatching trips, and in the news when a breeding site is threatened. Taiwan has terns too; the little tern breeds on some of the coastal sandbars.