© Philippe Verbelen
A bird paradise: hill forest on the remote Indonesian island of Peleng.
Tucked away in three of the most geographically isolated Indonesian islands of Wallacea, known for their unique and rich biodiversity, researchers have discovered 10 new species and subspecies of songbirds.

Found on the remote isles of Taliabu, Peleng and Batudaka off the north-eastern coast of the larger island Sulawesi, and described in the journal Science, it's the largest number of new species named in a region of that size in more than a century.

"Birds are so well-known as compared to other animals, so it was a major surprise to find five new species and five subspecies in such a limited geographic area," says lead author Frank Rheindt, from the National University of Singapore.

Around 11,000 bird species have been identified on Earth, and Rheindt estimates there could be another 100 undescribed ones worldwide.

After watching the feathered little critters since 2009, he tackled multiple challenges, including getting a permit, reaching the rugged islands and climbing mountains laden with equipment, to identify new species.

The team included Dewi Prawiradilaga and others from the Cibinong Science Centre in Indonesia. Rheindt's own discoveries were "mostly serendipitous", he says.

"Two of them were heard long before I was able to put my eyes on them. In one case - the Taliabu Grasshopper-Warbler [Locustella portenta] - it took me more than a week after first hearing it to finally see one because they are very shy."

Taliabu Grasshopper-Warbler
© James Eaton
Taliabu Grasshopper-Warbler
Other new species discovered on Taliabu - all at higher elevations - were named Taliabu Myzomela (Myzomela wahe) and Taliabu Leaf-Warbler (Phylloscopus emilsalimi).

Taliabu Leaf-Warbler.
© James Eaton
Taliabu Leaf-Warbler.
Three subspecies were also discovered here: Sula Mountain Leaftoiler (Phyllergates cucullatus sulanus), Taliabu Island Thrush (Turdus poliocephalus sukahujan) and the Taliabu Snowy-browed Flycatcher (Ficedula hyperythra betinabiru).

Nearby on Peleng, they found two new species, named Peleng Fantail (Rhipidura habibiei) and Peleng Leaf-Warbler (Phylloscopus suaramerdu), and one new subspecies, Banggai Mountain Leaftoiler (Phyllergates cucullatus relictus).

Just one new subspecies was identified a little further away on Batudaka: the Togian Jungle-Flycatcher (Cyornis omissus omississimus).

Togian Jungle-Flycatcher
© James Eaton
Togian Jungle-Flycatcher
The researchers chose these three islands because they have been largely overlooked by ornithologists. Another key reason for their focus on Taliabu and Peleng is attributed to the deep sea between them and Sulawesi, despite their geographic closeness to the main island.

"Sea depth is an important and long-neglected factor in determining the distinctness of an island's terrestrial communities," they write.

The islands would never have connected to the mainland during the Quaternary Period, isolating species and reducing gene flow and thereby increasing rates of extinction as well as proliferation of unique species.

In a related commentary, Jonathan Kennedy, from the University of Sheffield, UK, and Jon Fjeldså, from the University of Copenhagen, Denmark, note the importance of mapping global species diversity - particularly in remote regions - for understanding how life evolved.

With more than 80% of the earth's species still undescribed, this is also critical for estimating biodiversity loss and fuelling conservation efforts, they write.

Virtually every person on the planet should now aware that our planet is in crisis, says Rheindt, with its enormous, ongoing loss of biodiversity. These islands are no exception, being subjected to "rampant forest destruction" from logging and fires.

"We have limited resources to combat this," he adds, "but in order to conserve biodiversity, we must know where it is.

"Which are the islands that have lots of endemic species worth saving versus islands that are not particularly unique? The world needs a renaissance in biodiversity discovery, and quickly, before some of these species go extinct."