I HAVE often wondered how birds keep warm, why they have such attractive shapes and colours and why they fly so easily and with such grace.

The answer is all in the feathers. There are three basic types of feathers called down, contour and flight feathers.

Down feathers are soft and are the best natural insulators.

Then there are larger feathers which overlap each other like slates on a roof.

This allows water to run off literally like water off a duck's back.

These feathers also give the body its smooth shape.

Those who know of the parson's nose in a chicken but few know that this is actually an oil gland.

The bird spreads the oil onto the contour feathers and ensure that the water proofing is efficient.

The biggest feathers are on the wings and are known as the flight feathers.

The study of bird flight has always been difficult, but things have become much easier with the invention of high speed digital photography.

Nearly 40 years ago I got to know two of the world's best bird photographers and I remember the work of Eric Harking and Stephen Dalton.

Stephen Dalton's photograph of a starling flying out of its nest hole in a tree is still one of my all-time favourites.

These days the cameras make things easier, but capturing a bird in flight and displaying its flight feathers is still an art which very few photographers have been able to master.