Scientists and birdwatchers have discovered 10 new owl species in the Philippines, using advanced recording equipment that can distinguish between their hoots, a conservation official said.

Eight of the new species were previously considered sub-species while two are totally new, said Lisa Paguntalan, field director of Philippines Biodiversity Conservation Programme.

"There is no significant variation in their forms. It was the sound difference of their calls that was very significant in distinguishing between species," she told AFP.

Paguntalan warned that many of these new species were possibly endangered because they were found only in small isolated islands or in tiny pockets of forests.

Ornithologists and birdwatchers from Michigan State University, Birdlife International and other groups used museum samples and high-quality photography and recording systems to show the owls were of different species.

The research took 10 years but the results were only announced after coordination between the various groups.

The two new species are the Cebu hawk owl and the Camiguin hawk owl, found in the central Philippine islands of Cebu and Camiguin respectively.

They are described as about eight to 12 inches (20 to 30.5 centimetres) in size and hard to spot.

The Philippines is an archipelago of more than 7,000 islands with diverse animal species evolving in different parts of the country but many of these unique species are threatened by destruction of their habitat.