An international team of ornithologists has discovered a new species of ground-warbler on Luzon Island of the Philippine archipelago.

“The ground-warblers are very unique birds. They’re only known from the northern Philippines, and they have no close relatives,” explained Pete Hosner, a graduate student at the University of Kansas and a lead author of the paper describing the new bird in the Cooper Ornithological Society’s journal Condor.

“As the name suggests, they’re ground-walking songbirds and it appears that they can barely fly. They tend to inhabit dense forest understory, where they feed on insects. Their song is extremely high in pitch, and ventriloquial – it’s almost impossible to locate the source of the sound in the forest – they always sound like they are far away, even when they are almost at your feet.”

The new species is named the Sierra Madre Ground-Warbler. Its scientific name, Robsonius thompsoni, honors Max Thompson, a retired professor from Southwestern College in Winfield and a research associate in the University of Kansas’ Biodiversity Institute.

The bird looks similar to the other two species of ground-warblers in the Philippines, the Bicol Ground-Warbler and the Cordilleran Ground-Warbler, so it wasn’t recognized as an independent species at first.

“The three species of ground-warblers now recognized are essentially identical in size, shape and juvenile plumage coloration held in their first year of life, but they differ from one another in adult plumage coloration,” Pete Hosner said.

“The reason that this new species remained undescribed for so long was that the adult plumage of the very first ground-warbler to be described was unknown. That species, Cordilleran Ground-Warbler, was documented only from a single juvenile until our recent fieldwork. As a result, the ‘discovery moment’ was when we saw an adult individual of the known species.”

Examination of its DNA was key to differentiating the new ground-warbler once it was spotted in the field.

“When we noted the different plumage coloration between adult birds in the Cordillera and the Sierra Madre in northern Luzon, we sequenced DNA to determine if the plumage differences were individual variation within a species, or if the two plumage forms were also genetically diagnosable.

“We found that Cordillera and Sierra Madre birds were highly divergent in their DNA, almost as different as the distinctive Bicol Ground-Warbler in southern Luzon.”

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Bibliographic information: Peter A. Hosner et al. 2013. Phylogeography of the Robsonius Ground-Warblers (Passeriformes: Locustellidae) Reveals an Undescribed Species from Northeastern Luzon, Philippines. The Condor 115 (3): 630-639; doi: 10.1525/cond.2013.120124