Hector McNeil, who worked on Glenbuchat estate for 30 years, had admitted killing a raven, of which there are only two breeding pairs in Grampian.
Aberdeen Sheriff Court had heard the 56-year-old had poisoned gulls eggs, a food source for ravens, to protect pheasant and red grouse numbers.
The RSPB said the fine was too small to act as a deterrent to others.
McNeil was fined 350 for killing a common gull and a raven, 400 for keeping 118 common gull eggs and 100 for keeping a banned pesticide.
Elsie Ashworth from the RSPB said: "Our concern that a 350 fine for the specific charge of placing these poisoned bates out in the open is very unlikely to act as any sort of deterrent to other people that might carry out this sort offence.
"We believe it should be higher."
The RSPB claimed this was one of many cases but a spokesman for the Scottish Gamekeepers Association had said the case was not typical of the profession.
Sheriff Alexander Jessop said he had taken into account that McNeil had co-operated fully with the inquiry and that it was his first offence.
He said: "I appreciate that in your work as a gamekeeper you have a job to do to try and preserve the estate and to ensure the employment of persons on that estate that is compatible with rare species of birds.
"It must be a difficult line for you to draw but in this case you did cross the line."
McNeil's lawyer said the gamekeeper had taken the proceedings badly and had been signed off work with stress.