DURING the winter months cormorants (Phalacrocorax carbo) can be seen along the river Wharfe. The yellow gular pouch at the base of their bills and their green eyes are striking when caught in direct sunlight. For much of the year, the plumage of adult birds appears a fairly uniform black. Although closer inspection reveals an interesting black and brown ‘scaly’ pattern on their wings. As the breeding season approaches, adults of both sexes develop white flecks on the head/neck and a white thigh patch (see photograph).

Cormorants are social birds that congregate in breeding colonies. There are two sub-species in the UK (although with some hybridisation), P. c. carbo and P. c. sinensis. The former is the native species, that has tended to breed on steep rocky Atlantic coasts. On average it is slightly larger than P. c. sinensis, which originates from the continent and predominantly breeds on inland waters or shallow rocky coasts. On very close inspection, these sub-species can be differentiated by the angle at the rear of the gular pouch - with P. c. carbo having the more acute angle.

Although they are quite a timid bird, cormorants can be conspicuous when standing at the side of the river – or on a rock in the stream. Particularly so when they adopt their ‘classic’ pose, holding both wings outstretched. They do this to dry their feathers. Their plumage is somewhat water-permeable, holding less air than is the case for most other water birds and reducing their buoyancy. As a result, when swimming on the surface, they can be difficult to spot, as they ‘sit’ relatively low in the water. Often only neck and head are clearly visible above the water line. However, this low buoyancy combined with their large webbed feet means that they are superbly capable diving birds and catchers of fish.

Unfortunately, the combination of an almost exclusively fish diet and their excellent fishing skills brings cormorants into conflict with the angling and fish farming communities. Although numbers of cormorants were low in the middle of the last century, they have increased substantially (especially for the P. c. sinensis sub-species). This can be explained by reduced environmental pollution (particularly pesticides); the fact that they have no natural predators; and legislation that has given a degree of protection from human persecution. Consequently, the government issues licences – to those concerned with preserving fish stocks - allowing a limited number of cormorants to be shot – providing that certain criteria are met (e.g., demonstrating loss or real potential for loss, and that non-lethal methods of control have been tried). Perhaps this is why, despite their size, cormorants are unlikely to tolerate a close approach – taking to the air if disturbed, with much splashing of webbed feet on the surface of the water and what seems to be plenty of ‘huffing and puffing’!

Steve Westerman