After a six-week expedition in 2013 and 2014, researchers have now described five new species and five new subspecies of birds in Indonesia. The ten-taxa haul, published today in the journal Science, marks the biggest discovery of new kinds of birds in over a century.

The team, led by ornithologist Frank Rheindt, focused on three small islands. Reviewing previous collection expeditions, Rheindt noticed that the eleven past trips were either brief or limited to the coast. None had ventured far inland or to high elevations, leaving behind an opportunity for discovery, so Rheindt focused his trip on those understudied areas. But rising wildfire risk and logging activity on the islands is already threatening the birds’ habitat.

“Our world needs a new impetus, a renaissance in biodiversity discovery,” Rheindt tells Jason Gregg at Audubon magazine. “We need more of that now because we can only conserve what we know.”

Birds are considered a well-known wing of the map of life, and on average only five or six new bird species have been described each year since 1999. Per Audubon, the team made use of abandoned logging roads to climb 3,600 feet to reach their destinations: the peaks of Taliabu island’s tallest mountains. There, they spent mornings documenting birds caught in mist-nets, and afternoons recording audio of the birds’ calls.

Songs and genetics rather than plumage differentiates one species from another. The team would often hear a bird before they saw it. One of Rheindt’s most elusive and favorite discoveries was the Taliabu Grasshopper-Warbler, which has a song so bug-like that porters doubted his claims that it was actually a bird, he tells Gregg.

“They found 10 new things, which is remarkable,” the American Museum of Natural History’s ornithology curator Joel Cracraft, who was not involved in the study, tells the New York Times’ Karen Weintraub. “It really points to how little we actually know.”

Another possible key to the islands’ unique fauna is their location. The islands Rheindt visited are eastern satellites of Sulawesi, one of Indonesia’s four Greater Sunda Islands. Although they’re near the larger landmass, the small islands are surrounded by deep ocean, so they never would have been connected to Sulawesi by land.

“We were also particularly intent on visiting islands surrounded by deep sea,” Rheindt tells Tim Vernimmen at National Geographic. “Because they have not been connected to any other land mass during the ice ages, they are very promising places to discover species not found anywhere else.”

All ten newly described species and subspecies are songbirds, including warblers, leaftoilers, flycatchers, and one each of a thrush and a fantail. The majority of recent bird species discoveries have come from South America, but Rheindt believes that the 20,000 islands in the Indonesian Archipelago are full of potential, per Audubon.