Shags on the Isle of May


A shag with its own individual coloured and lettered ring.


Note the “extra” nesting material – a shoe above and below a paint brush !

Shags are one of the most intensively studies species of seabird on the Isle of May, with researchers putting in a massive amount of effort and time each year to ring and monitor this charismatic species. Sarah Burthe, one of the researchers from the Centre of Ecology and Hydrology (CEH) who is involved in long-term monitoring of the Isle of May seabirds, writes some more about the research taking place on shags:
“Shags are my favourite birds on the island, they have such beautiful black plumage with an iridescent green tinge, and I like the crest of head feathers that they get during the early breeding season. When you see the feathers on the back up close, each one has a darker edge which gives them a beautiful scalloped appearance, and their lime green eyes are simply stunning. Shags also have a lot of character and can be amusing to watch in the field. They can be pretty clumsy when they are jumping up and down the rocks to get to their nests- I have sometimes seen them stand on their own feet and fall over- and it’s also really funny to watch them bringing nest material up to their nests.
Shags take nest building very seriously and put a lot of care into building these impressive structures in amongst the rocks, mainly on the East and South sides of the Island. Nests are built mainly from sticks and bits of seaweed, and you can often see shags picking up sticks from the beach area at Pilgrim’s Haven. However, shags also pick up more unusual objects and weave these into their nests. We have found some pretty funny objects when we go round to check nests, including pieces of rope, an extension lead, an old piece of hose-pipe, old beer cans, plastic milk bottles, a sock, dead rabbits, a lapwing wing (the first record that year for the island!), dead puffins, pieces of seal skeleton, pencils, a small armless plastic doll, a small cuddly toy dolphin, a ballet shoe, a small plastic lobster (which appeared in a different nest the following year!) and a headless action man!!!! It’s best not to leave things lying around near the nests- the shags can be a bit of a pain when they take a fancy to our marker canes and flagging tape that we use to mark active puffin burrows! Maybe this also explains why we are always short of pencils…
The shag work forms part of the long-term seabird monitoring work that takes place on the Isle of May- this has produced an incredibly important dataset that stretches back for some species to the early 1970s and has enabled scientists to look at how environmental change such as climate warming are impacting the survival, population size and breeding success of seabirds in the North Sea. Shags are an interesting species to study because they are resident around the Isle of May year-round, unlike razorbills, puffins, guillemots and kittiwakes, and because their population sizes can change from year to year more dramatically than the other seabird species. In shags there can be “crash” years when lots of birds die due to severe gales and difficult foraging conditions in winter. A pair of shags can also produce up to four surviving offspring per year which means that numbers can increase quite rapidly if these offspring survive and start breeding too. Shags are also good to study because they are relatively easy to catch on the nest, which means that we can mark individuals quite easily and get good data on the condition of adult birds and on chick growth rates.
Indeed, every year since the mid-1990s the researchers on the Isle of May attempt to catch and colour-ring all the shag chicks that are accessible on the island- last year this meant ringing at around 500 nests, which is a lot of shag chicks! This means that most of the shags that you see when you visit have got a unique set of identifying rings on their legs- look out for the colour rings when you see shags standing around on the rocks. The birds get a standard metal ring with a unique number, so that if the bird is ever found dead it can be reported to the British Trust for Ornithology, and they also get a larger plastic coloured ring on the other leg. These rings come in a variety of colours: red, white, blue, green and yellow and have three letters engraved on them that can be easily read at a distance with a telescope. These colour rings mean that we can collect a lot of very valuable data from the shags. We can identify the male and female parents breeding at each nest and know how old they are, and we can then also monitor the breeding success of each pair in each year. We also know whether birds are breeding each year and can also estimate individual survival, and we know which birds are related to each other.
Several research projects are currently taking place on the shags, including a number of PhD projects linked with CEH and also Edinburgh and Aberdeen Universities, and post-doctoral work with Glasgow University. I am currently looking at how parasites are affecting shag survival and breeding success, looking at both ectoparasites (lice and ticks) and endoparasites (gut worms). Hanna Granroth-Wilding is a PhD student looking at how gut parasites are affecting the growth rates, survival and behaviour of the shag chicks- as part of her project Hanna is taking some interesting videos where she is looking at competition for food between shag siblings in the nest by measuring begging behaviour etc. Finally there are also two PhD projects taking place (Emily Barlow and Hannah Grist) looking at shag dispersal – another example of why colour ringing shags is so important. So, not only are shags very beautiful seabirds with interesting behaviours that are fun to watch, but they are helping scientists to answer a huge amount of questions about the factors impacting seabirds and about seabird behaviour.

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