The Common tern is a summer visitor to the Isles of Scilly, undergoing one of the greatest yearly migrations of any bird. It spends our winter south of the equator, off the coast of Ghana in East Africa. Then in March and April they make a several thousand-kilometre journey north to breeding grounds. The common tern is an elegant and graceful flier, that is most likely to be seen on boat crossings between islands, fishing around the coast, or flying to and from their breeding colonies. These are very noisy places, with a series of raucous “kreee-aaars” and “kierri-kierri” calls given on alarm, and loud chattering uttered when a partner brings in food.
The number of Common terns visiting the islands has been in steady decline for the last 30 years. In 1970, 200 pairs bred but now there are between 60 or 70 pairs and during 2010 none. The reasons for this decline is unclear, but predation from rats, gulls and crows, as well as disturbance from people are the major causes. Common terns often nest in very exposed places and sometimes nest on islands prone to high tides and bad weather, this results in the loss of eggs and chicks.
Historically the Roseate tern, Sterna dougallii, has nested in colonies with the Common tern and if the Roseate tern is to return to Scilly then maintaining a healthy Common tern colony is essential. The Roseate tern is one of Europe’s rarest seabirds, numbering around 700 breeding pairs with only 50-60 pairs breeding around the UK. Since 1840 Scilly was home to up to 12 breeding pairs but the last Roseate terns to breed was in 1994.
Since 2000 in conjunction with Natural England we have been implementing a Roseate Tern Species Recovery Programme and during 2004 – 2007 a project was undertaken to determine the breeding success of Common terns across the Isles of Scilly.
Terns can be difficult to identify unless you are lucky enough to get a good view. In general they are smaller than gulls and have a more dainty flight, and often dive for sand eels from a position hovering over the water.