The group said it is extremely disappointed by the Scottish Government's decision to allow the Balmedie development, which will affect environmentally sensitive dunes.
It acknowledged that a judicial review is not an option and said although the dunes are designated a site of special scientific interest (SSSI), they are not protected under European legislation.
The Scottish Government decided to grant outline permission following a public inquiry earlier this year, subject to satisfactory legal agreements. Finance secretary John Swinney said he agreed with the reporters on the project's significant economic and social benefits.
The scheme has been mired in controversy ever since it was narrowly rejected by Aberdeenshire Council's infrastructure committee last year and then called in by ministers (Planning, 7 December 2007, p3).
RSPB Scotland head of planning and development Aedan Smith said Trump refused to consider an alternative layout that would have avoided the SSSI.
"It appears that the desires of one high-profile developer have been allowed to override the legal protection of this important site. We fear that this sets a precedent that will undermine the whole protected sites network in Scotland," he said.
The scheme proposes two championship golf courses, a hotel, 950 holiday homes and 500 houses. The outline permission is subject to 46 conditions. These include an environmental and habitat management plan and a design review with the council and Architecture and Design Scotland. The extent of the coastal dune ridge has to be defined and protected from construction works.
The authority has three months to conclude the legal agreement with the Trump Organisation. Director of planning and environmental services Christine Gore told Planning that she hopes to move quickly.
Heads of terms already on the table cover affordable housing, education and community facilities, road improvements, an environmental advisory group and a jobs and training programme.
"It will be a package worth several million pounds for the community," Gore said. "Ministers have indicated support for the principle of this project but we need to work together on the detailed applications to ensure that it is as good as it can be."
Trump said his scheme would be a "source of pride for Aberdeenshire and Scotland". He hopes that work will start next year.
The decision letter is available at PlanningResource.co.uk/doc