We must all have seen a cormorant (Phalacrocorax carbo) doing this but why do they do it? Conventional wisdom says it is to dry their wings which obviously get saturated after they have been diving. This may well, of course, be very true but it raises the question that why do cormorants need to do it when other diving birds do not? You never see duck or grebes, for example, drying their wings after a fishing expedition. The answer could well be that the cormorant has much bigger wings and. as it spends more time flying than a duck or a grebe, then drying them out is more important.
I have, however, heard a theory that this posture aids their digestion. Cormorants swallow their catch whole, head first, and it takes a good while to get the fish right down the throat and in to the stomach. Holding out its wings like this opens the passage way and eases the flow. There may be truth in both of these.
The cormorant is very common on the land-locked harbours of Dorset; that is Poole harbour and Chrstchurch. They are also commonly seen on larger lakes and rivers, notably Radipole Lake in Weymouth. Along the higher, rocky cliffs of the Purbecks they are replaced by their more seafaring cousin, the Shag.