A rare giant Philippine eagle has been shot dead two months after being released back into the wild following treatment for another shooting, in a blow to efforts to save the species from extinction, conservationists said Wednesday.

The raptor's remains were found on a forest floor last weekend with a gunshot wound on its right breast, three years after it was rescued and treated, the Philippine Eagle Foundation said.

It was the 30th to be found dead or wounded out of an estimated population of just 400 pairs in the wild, which reside mainly on the large southern island of Mindanao, its executive director Joseph Salvador said.

"Unfortunately, one person with a gun thinks he can shoot anything," Salvador told AFP, adding no one has been arrested in the latest incident.

"The potential to teach people the importance of the eagles to wildlife and biodiversity has been compromised."

Famed for its elongated nape feathers that form into a shaggy crest, the Philippine eagle, one of the world's largest, grows up to a metre (3.3 feet) long with a two-metre wingspan.

The Swiss-based International Union for the Conservation of Nature lists the species as "critically endangered", due to the depletion of its tropical rainforest habitat and hunting.

Philippine eagles kill macaques and other smaller animals for food and need vast tracts of forest as hunting grounds, routinely driving away rivals from their territory.

Gunshots accounted for nine out of every 10 Philippine eagle casualties recorded by the foundation over seven years.

The latest bird to be killed had been rescued as a juvenile three years ago and treated for superficial gunshot wounds.

Returned to the wild in Mindanao's Mount Hamiguitan reserve two months ago, the eagle's carcass was tracked about a kilometre (half a mile) away from where it was released, after a fitted radio transmitter indicated the bird had stopped moving.

Killing critically endangered Philippine species is punishable by up to 12 years in prison and a fine of up to one million pesos ($21,600). Salvador said the foundation would press charges once the eagle's killer was found.

Guarding the bird, also called the "monkey-eating eagle", is compounded by inadequate forest rangers, with just six assigned to the vast Hamiguitan range, Salvador said.