Tomorrow will mark a celebration of important waterways, home to thousands of birds which migrate to Britain, and Norfolk, each year but whose numbers are declining.

World Wetlands Day, on February 2, signifies the importance of the world's network of waterways and wetlands which are home to millions of migratory birds each year.

And according to the latest Wetland Bird Survey (WeBS) report by the British Trust for Ornithology (BTO), based in Thetford, which aims to identify population sizes, trends in numbers, and distribution, the feathered friends are particularly partial to areas along the Wash, on the Norfolk and Lincolnshire coasts.

These hold almost 400,000 waterbirds each winter.

WeBS core count organiser at the BTO, Chas Holt, said it was important to study the causes of the birds' decline.

He added: 'Around 3,000 volunteers take part in monthly counts at wetlands across the country, providing us with the numbers that prove just how important the UK is for wintering waterbirds and ensuring that the sites they use are afforded protection for the future.

'However, it is starting to look like some of our wintering waterbirds may be in trouble. Numbers of many species are showing distinct declines.

'Whilst for some species, such as the European white-fronted Goose, this may be due to increased numbers wintering on the continent, for others it is looking like there may be declines across their range internationally.

'UK declines in ducks such as the pochard, velvet scoter and red-breasted Merganser are mirrored elsewhere across northern Europe, suggesting potentially serious changes in their environment.

'Whether this is due to conditions on the Arctic breeding grounds, along their migration fly ways, or in their winter quarters, is something that requires urgent investigation.'

Some of the birds which come to Norfolk's wetlands have been doing so for many years.

Longevity records show, for example, an oystercatcher trapped and fitted with a ring of the shores of the Wash was re-caught in almost exactly the same place 40 years, one month and two days later.

Mr Holt added: 'In Norfolk there's a lot of wetland habitat in a relatively restricted area, particularly along the north Norfolk coast.

'They offer a lot of habitat for these birds and it's close to continental Europe so it's a stop off point for birds like ducks and geese. 'You'd certainly notice it if the Wash lost a lot of its birds - the north Norfolk coast derives a lot of benefit from the birds in terms of the economy and the nature reserves.

'Going out to birdwatch is one of the most obvious parts of our wetlands and it's important for the general public to go out and appreciate them.'