Return to the estuary in winter - wrapped up warm with a thick coat, gloves and hat, perhaps with that new telescope or binoculars and identification guide you have just got for Christmas.

Thames estuary showing frozen 'sea'.

Estuaries are less saline than the open ocean as they contain a mixture of fresh water (from the river) and seawater so they are more likely to freeze. East coast estuaries are also more prone to ice and snow, depriving the over-wintering birds of their food. This means that estuaries in the west can be very important in hard winters, when birds from our east coast and the Low Countries come here.

Birds using Britain's estuaries are often long distance migrants that have bred far to the north in areas that are snowbound during the winter. They rely on our mild climate and rich food supply to survive until next year. But they are often on the limit of their endurance after a long, non-stop crossing of the rough northern seas.

So when you see a flock of waders feeding on the shore don't let your dog go and chase them. They may be recovering from a long crossing or trying to build up their reserves for the next leg of the journey, and so even a small amount of disturbance can mean the difference between life and death.

Watch the birds carefully as they can look rather similar in their winter plumage, check your identification guide for hints on the best way to tell similar species apart – is it by overall size, colour of legs, curviness of the beak or aspects of the plumage and don't forget to listen out for the bird's call.

Avocet – a success story, they recolonised the UK as a breeding species in the 1940's and now overwinter on estuaries where their thin upturned beak is ideal for feeding on the fine mud.

Looking at the birds you'll see that they have a wide range of different types of mouthparts. They vary in length by nearly a factor of ten from the curlew's very long curved beak to the short stubby beak of the turnstones and sanderlings via the strong chisel like red bill of the oystercatcher.

Each species specialises in a different type of prey, birds such as curlews and godwits can reach lugworms deep in the mud whereas sanderlings rush along just in front of the incoming tide picking food items off the surface. Turnstones, as the name suggests, turn over stones looking for invertebrates hiding underneath and oystercatchers either sneak up on mussels and stab them before they have time to close or hammer at a weak point on the side of the shell to smash them open.

If you watch the birds feeding on a estuary then you'll often see them with very muddy faces where they've stuck their beak right up to the hilt in the silt trying to find food.

Potential conflict between birds (curlews and oystercatchers) on a nature reserve and boat users in this very popular tourist resort in the south west of England.

What happens to the birds if an estuary is lost to development? This is a very difficult question to answer but also a very important one as most estuaries face considerable pressure from tidal barrage schemes, marinas and other forms of development. In a very careful study a group of researchers looked at the Cardiff Bay barrage where 200 hectares (just under 500 acres) of estuary were lost.

They found that the survival rates of redshank fell by 44%. Britain's mild estuaries hold overwintering bird populations from very large areas of the frozen north so by damaging our estuaries we are negatively affecting the bird populations in many other countries. We have an international duty to protect these areas as well as having the opportunity to go out and enjoy them ourselves.

All Images for this article supplied by Mike Dodd Photography. This article was originally published September 2006.

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