One glance at a black-headed gull (pictured) is enough to tell us that spring is upon us.

In winter the gulls moult out their black, or in fact dark chocolate brown heads leaving just a dark mark behind each eye.

Then, from late January they begin to acquire fresh plumage which includes the dark heads so that by March, most adults will once again show off their 'black' heads although some young birds are still at the transitory stage with patchy grey heads.

Soon, the gulls which have been thronging lakes and the riverside will gradually move off to their breeding grounds.

Only a small proportion of black-headed gulls actually nest at the coast with many choosing other sites including reservoirs, gravel pits and salt marshes and I remember some years ago in Wales one solitary pair nested on the side of a low mountain.

But it hasn't always been like this.

Black-headed gulls were mainly coastal birds until in the nineteen-twenties, there was a series of severe winters causing the gulls to move inland for shelter and when they discovered rubbish tips and reservoirs they never looked back and stayed around to nest in such places.

Herring gulls and lesser black-backed can also be seen along the Thames, on larger lakes and at the London Wetland centre all year round.

The so named common gull is now quite scarce but can be seen in winter along the Serpentine in Hyde Park and on the round pond in Kensington Gardens.