And species usually found in northern Europe, such as the fieldfare, redwing or Slavonian grebe, had become less frequent in Britain.

"The species are almost certainly responding to the changing climate," said Brian Huntley of Durham University in England of a report he wrote with researchers at Cambridge University and the Royal Society for the Protection of Birds.

The study tried to filter out other factors that would affect counts of rare birds, including growing public interest that could mean more sightings. Shifts in farming, pollution, expansion of cities and conservation efforts have all affected wildlife.

Birds and butterflies are among the first to adapt to climate change because they can fly long distances to seek a cooler habitat. Other creatures and plants can take far longer if their traditional range gets too warm.

"It depends on the mobility of the species. Birds and butterflies are two of the groups where there is the best evidence that species are already showing responses to the changing climate," Huntley told Reuters of the study in Royal Society journal Biology Letters.

GREENHOUSE GASES

The shifts in the birds' ranges since 1980 were also consistent with scientists' expectations because of global warming, blamed by the UN Climate Panel on human use of fossil fuels in power plants, factories and cars, he said.

The panel predicted last year that warming will bring desertification, floods, melt glaciers, raise world sea levels, bring big shifts in the ranges of species and extinctions.

"This gives us greater confidence in the climate models we use for other groups of species -- butterflies, plants, reptiles and amphibians," Huntley said.

"We rarely have the opportunity to test these kinds of models. We can only wait around for 50 years and wait to see if we were correct. It's better to have historic data" as a benchmark, he said. -- For Reuters latest environment blogs click on: http://blogs.reuters.com/environment/ (Editing by Stephen Weeks)