Creature feature: shag

Dinosaurs – shags and cormorants are pretty much the nearest thing we have to them here in the UK. As they sit on the rocks with their wings outstretched, regaining body heat, they really are reminiscent of a pterodactyl! When seen close up, their emerald green eyes are brilliantly piercing and it’s easy to see their lineage from the late Jurassic period.

A common question here at St Abb’s Head is ‘what’s the difference between a shag and a cormorant?’ Well, for starters, young cormorants and shags are both browner in colour than adults, but cormorants have a large white belly patch, shags a light brown one. Adult cormorants have a white patch on the face beneath the yellow (they also have white on their head and ‘hips’ in their summer plumage), while adult shags have small yellow patches at the base of the bill. Cormorants have thick sturdy bills with a big hook at the tip, whereas shags have slender, delicate bills.

For a short time early in the breeding season, shags also have a shaggy crest on the head (where they get their name from) but at this time of year it isn’t always visible. When seen at close quarters, cormorants are bluish-black in colour, with shags appearing more of a bottle-green colour, especially in the sunlight. They show iridescence (a shiny purplish green impression, similar to starlings) which comes from an oil excreted from a preen gland near the tail. We have fewer cormorants than shags here at St Abb’s Head but both do occur, so it’s always important to use a combination of features when identifying birds (or anything else for that matter!).

Shags are benthic feeders – this means they feed in inshore, shallow waters and find their prey (fish, sand eels, molluscs) accordingly. They struggle during stormy winters as high winds and swell stir up the seabed, making it much harder for them to find food. They’re prone to ‘seabird wrecks’ occasionally, events where conditions cause mass deaths out at sea and the birds wash ashore.

Interestingly, it’s possible to tell the male apart from the female ... and it’s not to do with their appearance. Although there are no distinguishable plumage differences, the male shag will give a low, croaking call when interacting with other birds, whereas the female is nearly always silent, only sometimes giving a muted hissing call. This is only helpful for identifying birds when they’re very close up, but it can be a handy way to tell them apart!

A great thing about shags is that they’re a relatively easy species to keep track of via ringing. Using large, coded colour rings, we can learn a lot about the life of an individual shag, which can then feed into understanding of the wider population. UK ringed shags have been found to live for over 30 years.

The numbers at St Abb’s Head have taken a mighty tumble – in 1991 there were 463 pairs; a count in 2019 revealed just 90 pairs breeding on the reserve. This staggering 81% decrease is an extremely worrying sign for the population. By monitoring these birds annually it’s hoped we can gain a better understanding of the reasons behind their decline.