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Reddish Vale Country Park

Cormorants are members of the pelican family and breed in close colonies, often consisting of thousands of birds. Large nests, made from twigs and seaweed are sited on cliff tops, ledges even in trees inland.

 

Cormorants eat mainly fish and eels, which are caught by diving and then swimming underwater. The most common stance of the cormorant is upright with its wings spread out to dry.

 

They are expert swimmers, floating low in the water, sometimes with only their head and neck showing. To dive they jump up and plunge head first, or just sink beneath the surface. They may dive down as far as 100ft and the longest recorded dive is 71 seconds. Usually they stay under for less than 30 seconds, swimming about 20-30 feet below the surface.

 

Cormorants are strong fliers, flying rather like a goose, with neck stretched out, head held up and rapid wing beats. They can soar in the air currents, but usually fly low over water.

 

Cormorants have sometimes been persecuted by fisherman because of the devasting effect they can have on fish stocks both at sea and inland waters. In the Far East, some fishermen make use of the cormorant's expertise, by training it to catch fish for them. A collar and lead is attached to the birds neck and the collar is just tight enough to prevent the bird from swallowing a captured fish. The fisherman retrieves the fish from the birds beak, only loosening its colllar now and then to allow it to swallow a fish.

 

Wing Drying.

 

After leaving the water cormorants nearly always spread their wing, often facing into the wind to help dry them, in very wet weather they don't spread their wings at all after leaving the water and in cold weather hold their wings out for longer, it's estimated they would have to use 222 kilojoules of body heat to dry them, wing spreading would seem to be a more efficient way of drying their wings. Most of the worlds 150 or so species of diving birds do not have to dry their wings, the answer, it seems, is the feather structure of cormorants and their close relations. Different diving birds adopt different strategies to enable them to get deep down under water. Like most creatures, birds are naturally buoyant. Cormorants are thought to swallow pebbles to increase their weight. Their main adaptation, though, is a much more open feather structure that does not trap buoyancy-increasing air but gets wet instead. Penguins, which dive to a remarkable 250 metres and can stay under for 15 minutes, do not get wet because their body feather structure is not as open. It is also designed to trap little air.

 

Regulating body temperature.

 

This one has been largely discounted, cormorants hold their wings out in the coldest weather, so why would they want to loose body heat at a time when all other birds are struggling to preserve theirs.

 

Digestion.

 

A study at a German zoo found cormorants fed cold fish held their wings out, often for 20 minutes. But fewer than a quarter of the birds fed fish pre- warmed to cormorant body temperature bothered to make a wing movement, and then only for a few minutes.

 

The implication - albeit using zoo-confined birds that did not dive and get wet - is that cormorants are exposing their bellies to absorb the sun's heat, a warm glow that aids the digestion.

 

There are other theories for the cormorants behaviour, one is they do it to keep other birds at a distance, or they do it to create a shadow so they can see the fish easier, another one is, they do it as a sign of fishing success. Unlike the cormorants wings, these don't seem to hold water.

Cormorant

Click on an image

Length, 77-94cm,

Wing span, 121-149cm

Weight, n/a

Lifespan, n/a,

Diet, fish.

Breeding pairs, 9000,

UK wintering 24,200.

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Cormorant