Climate change is disrupting the habits of birds which normally migrate to and from Britain in winter, the Royal Society for the Protection of Birds (RSPB) said on Friday.

With its relatively mild climate and ice-free conditions, Britain attracts over five million birds each winter from cooler climes such as Greenland, northern Europe and Siberia -- but the number is falling.

Warmer winters mean that some yearly visitors, including mallards, shelducks and turnstones, are choosing not to fly as far as Britain because they can find suitable conditions closer to home, the RSPB said.

"The UK has had both the perfect climate and perfect habitats for these birds, but the evidence is growing that climate change impacts are starting to bite," said RSPB Conservation Director Mark Avery.

"Sea level rise and warmer winters are reducing their numbers, undermining our importance for birds."

Other birds are now staying in Britain over the winter instead of migrating to warmer climates. The RSPB says the number of waterfowl species wintering in Britain has doubled in the past three decades as migration patterns change.