Wind farms can reduce bird numbers by up to half, according to a new study by the Royal Society for the Protection of Birds, that raises questions about the charity's support of the new technology.

A study by the RSPB found that wind farms reduce the number of breeding birds The study, in conjunction with the Scottish Natural Heritage, looked at 12 upland wind farms in the UK during the breeding season for a dozen common species including rare species such as hen harriers and skylarks.

The research, published in the Journal of Applied Ecology, found seven species were found less often than would be expected close to the turbines. The breeding population of buzzard, hen harrier, golden plover, snipe, curlew, wheatear and meadow pipit were reduced by up to half within 500m of the turbines.

It suggested that the most likely cause of the decline is the fact that birds are less likely to live near wind farms because of the noise and development, therefore the number of predators will also decline. Strikes with turbines was also suggested as a cause, but was thought to be less likely.

The RSPB recently came out in favour of wind farms, causing many members to leave in protest because of concern about the developments ruining the view in remote areas and contributing to the decline of birds.

However James Pearce-Higgins, senior conservation scientist with RSPB Scotland and lead author of the study, said charity still supported wind farms. But developments should not be put in the wrong area - where they can harm birds.

"There is an urgent need to combat climate change, and renewable energy sources, such as wind farms, will play an important part in this. However, it is also important to fully understand the consequences of such development, to ensure that they are properly planned and sited," he said.

"Our results emphasise the need for wind farms to avoid areas with high densities of potentially vulnerable species such as curlews and golden plover, and help offer a way forward by informing the likely extent of positive habitat management which may help to offset the impacts of development."