A rare peregrine falcon was shot dead with an air rifle at a reservoir.
The RSPCA is investigating the horror at Elton reservoir in Bury.
The bird of prey was found dead by a bird watcher who raised the alarm.
An x-ray later revealed it had been shot with an air rifle.
Peregrine falcons are the world's fastest living creatures and can reach speeds of 200mph.
They are heavily legally protected under the Wildlife and Countryside Act 1981 and adults nest in Manchester city centre and at Bolton and Rochdale town halls.
Warning: Graphic image below
RSPCA chiefs have issued an appeal for anyone with information about the 'disgusting' gun attack to come forward.
Inspector Paul Heaton said 'rumours' in the area suggested someone had been taking 'pot shots' earlier at wood pigeons around the reservoir.
The breed is making a slow return to Greater Manchester and peregrines are often seen hunting in the vicinity of the countryside reservoir.
The dead falcon - which had no leg ring attached and was living in the wild - was discovered last Sunday, May 12.
It's believed to have been dead for a day or two.
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Inspector Heaton said nesting pairs were now present in almost every Greater Manchester borough.
He said: "This is a lovely nature reserve which is popular with walkers, bird watchers and fishermen so I am asking anyone who saw anything suspicious to get in touch.
"There were rumours that someone had been taking shots at wood pigeons too prior to this so we would like to hear from anyone who may know who is responsible.
"This is such a horrible way to end the life of such a wonderful bird.
"Peregrine falcons are slowly making a return to the Greater Manchester area and are a fantastic bird to see. It is disgusting to think that someone would take pot shots at them."
All wild birds are protected under the Wildlife and Countryside Act 1981.
It is an offence to kill, injure or take them except under licence.
The RSPCA said the maximum penalty, if a suspect is found guilty, is six months in prison and/or an unlimited fine.
Call the RSPCA appeals line on 0300 123 8018.
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