The RSPB said about 300 hectares of its reserve at Loch Garten, Abernethy, had been burned and teams were still working to contain the fire.
The charity said there was “a huge community effort” to halt the spread with gamekeepers and other staff from neighbouring estates.
There had been concerns for capercaillie – large woodland grouse – that have recently been spotted around Ryvoan.
Parts of Scotland remain at very high risk of wildfire over the weekend.
The SFRS, in conjunction with the Scottish Wildfire Forum, issued warnings for the central Highlands, southern and eastern Scotland.
The alert lasts until Monday following days of hot and dry weather in many parts of the country.
SFRS area Commander Lynne Gow said: “We want people to enjoy the outdoors safely, but during periods of heightened wildfire risk we are asking everyone to act responsibly and avoid the use of naked flames.
“Wildfires can develop rapidly, spread unpredictably and have devastating consequences for communities, wildlife and the environment.
“By taking simple precautions, everyone can play a part in helping prevent further incidents.”
If you see a large outdoor fire, call 999 immediately. Give the location and any other relevant information so fire crews can respond quickly.