Wednesday, 3 June 2015

The science of counting sea birds

Many people have asked me how we know how many sea birds are breeding in the Nature Reserve here at St Abb’s Head. The simple answer is we count them all!

There is a lot of method to what, at first though, seems like madness. Firstly, the cliffs are split into manageable sections; there are 25 at St Abb’s Head. The boundaries of the sections are marked on a map which gives a birds-eye perspective and this is supported by a series of photos taken from sea which clearly shows the section boundaries. However it can still be quite challenging to understand these maps when you are working from the shore.

Each year the total number of herring gull, shag, fulmar and kittiwake nesting on the reserve are counted from the shore; this is supported by taking a small boat out to count the areas that can only be seen from the sea. But what about the auks? Well, as the guillemots are so numerous a whole colony count isn’t undertaken every year, the last one was completed in 2013. Every 15 years or so there are national schemes that aim to count all the breeding sea birds in the UK, and the whole colony counts for the guillemots and razorbills are normally done in conjunction with these. However in between these counts, 5 plots of each are counted every year. This then allows us to monitor any fluctuations in the number of birds from year to year.

So, in answer to the initial question, we have 42,900 breeding sea birds at St Abb’s Head, which can be broken down by species to:

  • 33,000 Guillemots
  • 7,250 Kittiwakes
  • 1,820 Razorbills
  • 370 Herring Gulls
  • 230 Fulmars
  • 210 Shags

And if counting all those sounds like a lot of work, we also monitor the breeding success of the shags and kittiwakes, and more recently the guillemots and the razorbills. This is done by following nests from eggs being laid, to chicks fledging. For the shags and the kittiwakes, visits are made every 7-10 days. The guillemots and razorbills however need to be visited every 1-2 days, and that is my job.

So I have been following 100 guillemot nests since the beginning of May and 50 razorbill nests from the middle of May. The challenge to begin with is that neither guillemots nor razorbills actually build anything that resembles a nest, instead they lay an egg straight onto a ledge which is pear-shaped to prevent it from rolling off. The egg is rather large for the bird, but it is expertly tucked away under the birds, so it is out sight from the preying eyes of herring gulls. So actually establishing what is a nest and being able to find it on each visit is actually quite a challenge. To give you an idea have a look at the map I use to relocate the nests on each visit for one of my plots.

To do this I use a spotting scope and sit at the edge of the cliffs. This means that if it’s raining or very windy I can’t collect the data for obvious Health & Safety reasons. This can lead to a bit of frustration when the weather just isn’t playing ball, as I want to collect as much data as possible to get the most accurate results I can. All this sea bird monitoring means May and June are busy times for the rangers at St Abb’s Head. So give us a thought as we obsess over weather forecasts, but most importantly on a sunny day come and see the sea birds for yourself. We have kittiwakes and razorbills all sat of eggs, the guillemot and herring gull eggs have begun hatching and we have shag chicks, some of which are now quite big!


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