The Viking Energy project, for 150 turbines, is a joint venture between Scottish and Southern Energy and the island community.

It has been estimated the project could make £37m a year locally and create many jobs.

Now RSPB Scotland has added its voice, on the grounds of possible bird species impact, to local resistance.

Populations of birds, including the golden plover, could be threatened by some of the turbines, RSPB Scotland said.

'Review position'

RSPB Scotland's head of conservation policy, Lloyd Austin, said: "We very much appreciate the consultation the developers sought with us at the early stages of the design and the effort they have taken to avoid SSSIs and other protected areas.

"However, now we have analysed the full detail of the application, it is clear a wide range of bird species will be impacted.

"However, we would be prepared to review our position if these issues could be satisfactorily resolved."

Land conservation charity, the John Muir Trust, last week urged people to object to the plans.

The trust said the development would "significantly affect" about a fifth of mainland Shetland.

More than 3,500 people are said to have signed a petition against the plans.