The watery world of the cormorant

Wherever you look, wildlife is under threat from human activity and many animal species are experiencing deeply concerning declines in numbers.

There are, however, a few exceptions. One such outlier is the cormorant, a bird at home on the water; an expert diver and fisher, which has seen its UK population explode in recent decades.

The name cormorant is derived from the Latin corvus marinus, which translates as ‘sea raven’ – due to its size and dark feathers. And while cormorants are associated with the sea, they are found in other watery habitats.

Britain’s native cormorant is mostly confined to the coastal rocks of western Britain but its continental cousin prefers to roost in trees - building nests of seaweed, reed and twigs. It is this sub-species that has spread from Europe - thanks to protective legislation against persecution – and can now be seen in high numbers not just on the east coast but increasingly on estuaries and inland waterways in the region.

I regularly see them flying over Sudbury’s Common Lands – their short wings powering them non-stop like black darts towards their next watery destination.

Low swimmer

Once in the water, they swim incredibly low, the water almost washing across their back. They resemble a submarine about to resurface – their long neck and large beak with a hook on the end playing the part of a sinister periscope.

They certainly submerge like submarines - no nonsense, just point the beak down and the sleek body follows. Some sea-based cormorant species from across the world have been known to dive as deep 150 metres. Obviously, on the Common Lands they do not reach anywhere near that depth, but I have watched one bird stay under for an impressive 30 seconds or so – reappearing some distance from where it had taken the plunge.

Research has shown that the cormorant’s ears and eyes are adapted for prolonged periods underwater although the bird does not see with much more clarity than humans below the surface. Instead, they rely on swimming fast and far in the hope of coming across prey that can be grabbed at close quarters.

Turquoise jewel

Cormorants’ ability to catch fish is well-known. The bird will tackle fish of all sizes, even large pike, and has an incredible ability to open its throat to gulp them down whole. Sudbury nature photographer Ron Smith recently caught some stunning footage of a cormorant doing just that.

The cormorant is not what you could call a classically attractive bird. When it stands with its wings outstretched there is something prehistoric about it – and this modern-day pterosaur has very little colour. Our cormorants are mostly black, sometimes with white patches on the belly and sides, and a small flash of yellow on the jowls showing the way to its lethal beak. But it is the eye of a cormorant that catches the breath – a stunning fierce and staring turquoise jewel placed within a mass of black feathers.

Crucifix

Cormorants are renowned for their classic ‘crucifix’ posture, where they hold their wings stretched out to each side. From a distance, their dark form resembles a giant bat, and the effect is amplified if they are striking the pose in a tree.

Research has shown that the structure of cormorant’s wing feathers means they get wetter than many other species of water bird. But far from being a disadvantage, this tendency to sogginess makes the bird less buoyant and better suited to diving deep and staying underwater. The upshot is they need to dry their wings in between dips.

There are a host of theories as to the additional benefits of spreading the wings in this way. Some say it enables cormorants to warm up quicker once out of the water – its black feathers soaking up the sun’s rays. Others posit that the stance – standing upright with wings back, chest puffed out – helps cormorants digest their food better.

So, the next time you feel a bit of indigestion coming on, you know what to do!