This week saw the return to Dun to look at how well our puffin colony has been doing over the summer. Myself and Neil went over in May to mark 100 burrows which had eggs laid in them, and we headed back over on Thursday, as this should be about the time that chicks should be getting close to fledging. The idea was to find out how many of those eggs had survived to become chicks that would be capable of leaving the burrows as healthy puffins, a measure of breeding success.
However, as soon as we entered the colony we could tell that something was wrong, as we saw dead downy chicks scattered on the ground in front of us. As we started to investigate each marked burrow our hearts sank, as we were finding burrow after burrow with either no chick or a dead one lying in the nest. In the end, only 26% of the burrows had live chicks in them, and many of these were severely underweight. Previous studies have shown that the figures generally come in at around 71% on St Kilda, with only one poor year over the study period when productivity was down to 44%. So, this is the worst year ever in terms of breeding success over the time they have been studied.
Dead puffin chicks in the colony
So what is going on here? All the dead chicks outside the burrows had no fat on them and predators hadn't touched them, suggesting that they had starved to death. A large part of the diet of puffins and many other species of seabirds is usually made up of sandeels, a highly nutritious fish of just the right size to feed a young chick. However, we have noticed for a while that the seabirds here have been bringing in pipefish (which look like a sort of elongated sea horse) to feed their young. This is a really poor sign, as they have almost no nutritional value whatsoever, and at an average of 25 cm long getting this down a chick is no mean feat! Pipefish were all over the ground throughout the colony this year, and many of the burrows were full of piles of rotting pipefish which the young were unable to eat. So, it looks like the puffins have been unable to find enough decent food to maintain their chicks which are then simply starving.
Neil with a live chick which is attempting to digest a pipefish
The only conclusion we can reach is that sandeels here, in common with much of the rest of our seas, have been extremely thin on the ground and that in desperation the birds are turning to other sources of food. It is believed that climate change has caused the temperature of the seas to rise significantly over the last few decades, which has caused the plankton that the young sandeels feed on to decline, with the final result that the sandeel stocks have plummeted. We've been hearing lots on the news about the seabirds in Orkney, Shetland and the East Coast suffering, but it was an especially sad day for us here to see that the St Kilda colonies are being hard hit too.
Sarah, Seabird and Marine Ranger