Fewer migrating ducks, geese and wading birds are wintering in the UK because more are staying closer to their Arctic breeding grounds due to climate change.
Many birds who migrate to the UK are staying closer to home
New studies by the British Trust for Ornithology (BTO) and the Wildfowl and Wetlands Trust have revealed the fall.
Teams patrol watersides in winter to count species and numbers of birds.
Their work covers the Wash, Morecambe Bay, Norfolk coast, Solway Firth and the estuaries of the Humber, Thames, Dee and Mersey in the period 2001-04.
Ducks, geese and waders are attracted by the relatively warmer winter conditions in the Gulf Stream protected British Isles but, claims the BTO, global warming could be persuading migrating birds to stay in cooler northern and eastern waters.
Britain is the winter home for about 10 million wetland birds and the Wash sees populations of 350,000, while other sites and the estuaries have numbers of more than 100,000.
However, heavy development of traditional sites in the south of England have seen loss of habitat which has caused the bird populations to move away.
Signs are growing that all is not well for a range of geese, ducks and wading birds.
For species such as the grey plover and dark-bellied brent goose, whose populations peaked in the early 1990s, after long periods of increase, numbers are now declining steadily.
But numbers of little egrets, pink-footed geese, gadwall and black-tailed godwit are all reaching record levels.
Andy Musgrove, of the BTO, who is the wetland bird survey national co-ordinator, said: "Different species are changing in numbers and one possibility is redistribution due to climate change.
"Milder winters mean many species spend winter closer to their breeding grounds so a decreasing proportion of their populations migrates as far as the UK."