Researchers led by the Michigan State University confirmed that two new owl species have been discovered after a study of their vocalisations found that they were new species and not subspecies.
The first is a blue-grey eyed owl, the Camiguin Hawk-owl, found only on the small island of Camiguin Sur, close to northern Mindanao.
At night, it gives a long solo song that builds in intensity, with a distinctive low growling tone. Pairs of owls give short barking duets that start with a growl.
The second new discovery was the Cebu Hawk-owl. This bird was thought to be extinct, as the forests of Cebu have almost all been lost due to deforestation.
"More than 15 years ago, we realised that new subspecies of Ninox hawk-owls existed in the Philippines," lead researcher Pam Rasmussen, Michigan State University assistant professor of zoology, said.
"But it wasn't until last year that we obtained enough recordings that we could confirm that they were not just subspecies, but two new species of owls," she said in a statement.
"The owls don't learn their songs, which are genetically programmed in their DNA and are used to attract mates or defend their territory; so if they're very different, they must be new species," Rasmussen said.
"When we first heard the songs of both owls, we were amazed because they were so distinctly different that we realised they were new species," she said.
The discovery was featured in the current issue of Forktail, the Journal of Asian Ornithology.