EVERY so-called "serious" birdwatcher has a favourite bird.

Mine has long been the Eider and I have studied it for more than 40 years.

We all know of an Eiderdown, but we have now discarded these in favour of our duvet.

We need not worry however, because eider in French is duvet and simply means of diving duck!

The male is beautifully coloured in contrast to his dull brown mate.

He does not help to incubate the eggs and so his black, white, green and pinkish plumage is for display only.

The female in contrast is ideally camouflaged and sites her nest in the underground around the colonies.

The duck pulls down from her breast and this is said to be the most efficient natural insulator in the world. Hence the word eiderdown.

Another fascinating aspect of eiders is that it is able to drink seawater.

Just behind the eye is a structure called a salt gland.

This separates the salt from the water which it then absorbs into its blood.

The concentrated sea water is then passed out of the gland via a nostril.

Despite studying the eider for many years, there are still new things to be learned and this is true for all birds.

This is what makes the subject so interesting.