Yesterday I took a trip to the Farne Islands on Serenity II skippered by Andrew Douglas. One of many highlights was seeing the arctic terns (Sterna paradisaea).
This delicate-looking bird undertakes the world's longest migration, flying 25,000 miles a year to and from its "winter" home in the southern hemisphere although, of course, it experiences two summers each year. In the course of its lifetime it will cover well over half a million miles. Fifty per cent of birds live for more than 30 years.
Arctic terns mate for life and usually return to the same nesting ground year after year. They nest side-by-side with common terns on the Farne Islands. Some of the nests are on the footpath and are vigorously defended against visitors.
The female lays one or two eggs (sometimes three) and some have already hatched. The chicks are fed by the parents for a month but then have to learn to fish before leaving with their parents on migration.
Watch a BTO video on identification of arctic and common terns here. Listen to the BBC Radio 4 Tweet of the Day on arctic terns here.