That’s a popular question and until this week I couldn’t say for sure as I hadn’t explored the data. Time for a quick recap... Back in May, Andy and I nipped over to Dun and marked occupied puffin burrows that had an egg inside.
We returned in July to relocate these burrows and find out how many now contained a chick. With this data it is possible to get an idea of just how successful the puffin breeding season has been.
Back in 2006 when the breeding season was spectacularly poor there were dead chicks scattered throughout the colony. Not this year, thankfully. However, many of the marked burrows showed no signs of activity and vegetation had grown over the entrances.
Birds were wheeling around carrying silvery fish, a good sign that the adults were finding the right kind of food to give to their young.
We collected a sample of fish from inside burrows and these were identified by Mike Harris (CEH) as nutritious rockling or sandeel. Unfortunately, all of the fish were quite small which suggests, perhaps, that the birds weren’t able to find the correct size class of items to provide to their young.
Each chick was quickly weighed and measured as these data can be used as a proxy for condition which then allows comparisons between breeding seasons.
Weights were lower than at this time last year and it was obvious that the chicks were at various stages of development; some were still entirely covered in fluffy down...
...while others only had a tiny bit of down left on their body...
You’ll notice that these young birds do not have the ‘characteristic’ colourful beak or feet that adults have. These features develop with age; the bill becomes more brightly coloured and distinctively marked and the eye ornaments get larger and brighter with each breeding season.
Anyway, back to breeding success..... Puffins extend their burrows throughout the season and because we forgot our ‘go-go gadget arms’ we were unable to tell whether some burrows had chicks in them.
Because of this we can’t calculate an exact productivity figure but can confidently say breeding success was in the region of 42-49% this year. Given that a reasonable year is considered to be one with a productivity value of around 70% it seems likely that the puffin colony on Dun had a poor/moderate breeding season. The below average weights of the fledgling birds that grounded themselves around the buildings agree well with this productivity value. Fish samples were relatively small and it is possible that, although puffins were able to find the more nutritious species, the size of items provisioned to young was not ideal and this could have impacted their weight gain.
But, on a more positive note, it could have been worse and this year wasn’t as disastrous for puffins as some others. It also shows the importance of gathering a range of information (weight of chicks, fish samples, weight of fledged young) to improve our knowledge of what is happening with the population of this iconic species.