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Ups and downs in the seabird season

30 August 2007

Well, it’s about the time of the year when we finally have a good idea of how the season went for the seabirds on St Kilda, and it seems to have been a bit of a mixed year really.

Guillemots seemed to fair much better than at many other sites around the country, where reports from Handa and the Isle of May suggested disastrous breeding seasons. Feeding studies I carried out on a Kilda colony showed that our birds managed to find some nutritious sandeels and herring-type fish early on in the chick-rearing season, which gave chicks a much needed boost, but towards the end of the season unfortunately many snake pipefish started appearing. These long bony fish, which look like elongated seahorses, have very little nutritional value and can actually choke the chicks. They have undergone a population explosion around the coast of Britain in the last few years, probably due to changes in the sea surface temperature brought about by climate change, and they are bad news when adult seabirds try to feed them to their chicks. However, it seemed that most of the guillemot chicks managed to leave the colony successfully, despite their poor diet at the latter stages.

 

1 guillemot

 

Guillemot diet study site

 

Puffins, which fledge several weeks later, weren’t so lucky. Although adult puffins were seen bringing in sandeels for the first few weeks after the chicks hatched, pipefish started to dominate the diet later on, and many chicks died from starvation in the colony that I study on Dun. Only 40% of eggs laid turned into healthy chicks that would fledge this year, the second worst year on record (in an average year, around 70% of eggs should produce fledgeable chicks). Those chicks that survived were also significantly underweight. It seems likely that puffins on St Kilda have had below average breeding years for a while, which has worrying implications for the future of the colony long term.

 

1 pipefish

 

Pipefish bundle pulled from puffin burrow

 

Kittiwakes also had a poor year, with only 30% of nests producing young that fledged, and once again this seems likely to be down to poor food supplies. However, it wasn’t all doom and gloom, as we had a record year for arctic skua nests, with two territories each fledging a single chick. Arctic skuas only started nesting on St Kilda in 2000, and they have a hard time defending their eggs and young against the many great skuas around, so it was heartening to see two successful nests, as these graceful and spectacular aerial acrobats never fail to delight.

 

Sarah, Seabird and Marine Ranger

Photos by Samantha Dennis



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