Dozens of firefighters tackled two moorland blazes spending hours at the sites on the Lancashire-West Yorkshire border over the bank holiday.
One of the fires - thought to have been started by a discarded cigarette - engulfed 300 acres of Marsden Moor, the National Trust said.
A separate fire near Baitings Reservoir in Ripponden, had been fanned by winds.
Gemma Wren, the countryside manager at Marsden Moor said many birds had been threatened by the fire.
The Marsden Moor fire at Scammonden, near Huddersfield, caused widespread damage to the land and endangered the lives of nesting birds and other wildlife in the area, the National Trust said.
Ms Wren said: "We have yet to fully gain access to the area following the fire but I'm already saddened by the prospect of what faces the team up there.
"It is likely that a carelessly discarded cigarette has caused this fire and I urge all visitors to think more carefully when travelling across the moor, to extinguish cigarettes responsibly and also take all rubbish home with them.
"The moor is a Special Protection Area for birds and where the fire broke out, we know that nesting birds including curlew, golden plover and twite will have been affected.
"We can only hope that some escaped the blaze and will be able to nest again."
Meanwhile, the Ripponden blaze spread at least two miles alongside the A58 towards Littleborough near Rochdale, Greater Manchester.
A fire service spokesman said rain dampened the blaze overnight but small pockets had remained alight into Tuesday. He said about 30 crew members remained there.
Crews set up fire breaks to stop the blaze spreading but were hampered by blustery winds. Keith Robinson, of West Yorkshire Fire and Rescue Service, said two fire officers were slightly injured tackling the flames.
He had to pull firefighters off the moor on four occasions as the wind changed direction and put them at risk.
Earlier on Monday, there were fears homes in Littleborough could be threatened but fire crews later said no property was under threat.
Smoke from the fire could be seen from the M62 motorway and was being blown into Rochdale and Oldham in Greater Manchester.
The cause of the Ripponden fire is under investigation.
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