Seabird populations in Shetland have had a disastrous breeding season this year, with some species having the worst results on record and the 700 breeding pairs of terns in Mousa failing to produce a single chick.
A UK-wide report published by the RSPB this week reveals that in Shetland terns and kittiwakes in particular have suffered, with some not returning to the nesting sites and some abandoning their chicks.
Numbers of guillemots, puffins, Arctic skuas and great skuas (bonxies) are also down.
RSPB Shetland South warden Helen Moncrieff said that the breeding failure of the terns was due to lack of food, sandeels, at the critical time.
Ms Moncrieff said: “If the terns have not got the energy and are not in good condition before the breeding season and if food’s not available they won’t breed – do they risk their own survival to bring a chick into the world?”
Tirricks come back to the same breeding grounds annually after wintering in the Southern Ocean. As surface feeders they rely, as kittiwakes do, on finding sandeels in the top few inches of water. These were not present this year, Ms Moncrieff said, and scientists have suggested this was because sandeels were lower in the water column after the long, cold winter. This favoured diving birds such as shags which by contrast have had a “really good year”.
Although terns and other seabirds have bred elsewhere in the UK, Ms Moncrieff described the picture in Shetland as “upsetting”. “It is worrying for Shetland as it is so important for seabirds internationally. Seabirds are an indicator of the health of the marine environment.”
Last year there were 900 breeding pairs of tirricks in Mousa which produced 400 chicks, she said, and this year should be seen in the context of many years. “Long-term monitoring is so important.”
The RSPB report showed that in Orkney the situation was “similarly miserable” for terns. In one reserve, only 356 pairs returned to a site that held over 3,000 pairs in the early 90s.
Just two kittiwakes returned to breed and not a single chick fledged there. And a comprehensive survey of great skuas in Orkney shows that nearly a quarter of the pairs present at the beginning of the decade have disappeared – a decline that represents three per cent of the global population of this species.
RSPB reserves ecologist Doug Gilbert said: “Although 2010 has been a patchy year for seabird breeding, the terrible season for the critical colonies in the far north warns us that seabird populations in the UK remain in real danger. This is against a backdrop of long-term decline for many species. Such declines are an indictment of our stewardship of the marine environment.”