Friday 17th April comments: As mentioned in the previous blog post, terns can benefit from man-made tern terrace structures and it’s not just Sandwich Terns, as the smaller terns also benefit including Common and Arctic Terns.
Common Terns are lesser known (in Isle of May terms) compared to their cousins the Arctic Tern, as the small numbers which nest can only be found away from the main public areas. The species has a circumpolar distribution and is strongly migratory, wintering in coastal tropical and subtropical regions. They are similar in size, structure and colour as the Arctic Tern but for one main feature, their beaks (known as bills). The bill of a Common Tern is mostly red (similar to an Arctic) but has a subtle difference; it has a black tip unlike its cousin.
Common Terns arrive at the May in late April having spent the winter off the west coast of Africa and generally nest on any flat, poorly vegetated surface close to water, including beaches and islands and will readily adapt to artificial substrates. On the Isle of May birds have responded well to the artificial tern terraces which have been constructed near the Beacon with 51 pairs nesting last year (an increase on the previous season). Birds can have clutches of up to three eggs and like most Tern eggs, are dull in colour with blotchy patterns to help provide camouflage in open areas vulnerable to predation. Both sexes will incubate the eggs for 21-22 days and it will take another 22-28 days to fledge chicks. Like most terns, the species feeds by plunge-diving for fish, either in the sea or freshwater.
As with the other terns, birds start departing the island in late July and by mid-August can be found fishing in the surrounding waters. As summer starts to slip away, birds gradually move south and by mid-September the vast majority are heading south back to wintering grounds in the southern hemisphere. And there you have the annual movements of the Common Tern and soon we’ll have them back with us as they wing their way north, to start their summer breeding season. Life goes on…