The European Shag - Planet Earth Online

Sue Nelson is off in search of the disappearing European shag, which is a sea bird similar to a cormorant....
04 December 2011

Interview with 

Hannah Grist, University of Aberdeen


A cormorant


Hannah -  A lot of research has been done on puffins and a lot less has been done on something like the European shag because people see it everywhere and don't think it's a really fascinating sea bird.  But actually, we've learnt a lot using the European shag system!  On the Isle of May we've been looking at them for about 30 or 40 years now, so we've got a lot of data behind us that we can use to answer a lot of questions.

Sue -   And what questions are you particularly posing?

Hannah -   Well, the thing we’re looking at the moment is because a lot of the work that we've done on the Isle of May has been during the breeding season, which is when they're breeding, obviously, but what we don't really know is what's happening to them over the winter period.  This is half the year for birds, so it's ridiculous we're not really paying attention to what's going on over this time.

Sue -   Is that because they disappear or because they stay there and keep out of sight?

Hannah -   Well for European shags, for the Isle of May population, what we think they're doing is that a proportion of the population are staying on the Isle of May over the winter and the rest of them are travelling up and down the coast, up to 200, 300, 400 kilometres away from the Isle of May and staying the winter in different locations.  And what we're really trying to do is find out why they're making that journey and what kind of effect it has on them.

Sue -   How do you do that then?  Do you ring them?

Hannah -   Yes! All the shags on the Isle of May are actually colour ringed.  They have plastic rings on their legs that have a three letter code on them and are brightly coloured.  And this is basically what we're looking for using the telescope is that we can read the code from distance, we don't have to recapture them, and it means that over the winter we can try and find them and see where individuals are and then relate that back to what we see on the island.

Sue -   I know this research project is ongoing but what have you found so far, any surprises?

Hannah -   I think the surprise is just the sheer distances that some of these birds are going. Also we're looking if there's any kind of segregation within the populations so, for example, partners might be moving together or offspring are moving together, and we're not really sure if that's happening at the moment yet, but we have had some anecdotes of partners being seen courting in different locations and juveniles from a single nest having stayed together, so these are the interesting things we can be looking at in the future.

Sue -   Do populations of European Shags tend to stay stable?

Hannah -   Shags are actually quite an interesting sea bird because they seem to follow a what we call a 'boom and bust' dynamic; they bred quite fast for long-lived birds, but they can also have really high mortality rates.  So over the winter in particular, we can lose huge numbers of the population in what is called winter wrecks; and in and around 1993-94 we actually lost about 90% of the Isle of May population in a really bad winter.

Sue -   That does make it odd then! Why do only some of the birds leave? Why don’t all of them go? Particularly when you can get very harsh winters...

Hannah -   The winters are harsh all the way along the east coast and we don't see so much of a kind of boom and bust effect on the west coast - we think because there are more inlets on the west coast and they can be more sheltered. So shags are really interesting in that - for a sea bird - and they're diving sea birds, they go for fish - they're actually not waterproof.

Sue -   A bird that isn't waterproof?

Hannah -   I know that's one of those things that sounds like a really terrible idea, but in fact they drive really deeply for birds that just go from the surface and dive down; they can get down to about 40 metres and the thought is that this kind of lack of waterproofing enables them to dive deeper, but what it does mean is that they're very restricted to being able to come back to land to roost - because they need to be able to dry out their feathers - and on this unsheltered eastern shores we think if we're having bad winters what's happening is that they just can't dry out sufficiently and that they might be losing them through hypothermia or really high costs of trying to keep themselves warm.

Sue -   What use will this information be, apart from the fact that you might be able to apply it to other populations of European shags in Wales and Cornwall and other areas where it's quite rocky and cliffy where they like to be?

Hannah -   Because it's such a long data set we've got on this population and we know the individuals, we're in quite a unique position to be able to look at things like, something we call a 'carry over' effect, which is the effect that perhaps staying in a particular location has on the breeding success in the future season and that's not something many people have been able to look at; but also from a shag perspective if we know key locations where they are more protected, where they are surviving better over the winter. So that's something that perhaps in the future we might be able to protect for them.  So from a conservation prospective it could have applied relevance.

Diana -   Hannah Grist from the University of Aberdeen.


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