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Sierra Madre Ground-Warbler Robsonius thompsoni (upper) was discovered after two years of elusive expeditions in Northern Luzon, the Philippines. The 10-cm-tall bird had earlier been confused for its close cousin, Cordilleran Ground-Warbler Robsonius rabori (lower).
Illustration: Marco A. Mr. Pineda / The Condor
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Abstract
The Robsonius ground-warblers are forest birds endemic to the Luzon Island complex in the Philippine archipelago. Their systematic relationships have long remained ambiguous; until recently they were included in the timaliid genus Napothera. Two Robsonius species are currently recognized on the basis of plumage differences: R. rabori from northern Luzon in the Cordillera Central and the northern Sierra Madre, and R. sorsogonensis from southern Luzon and Catanduanes Island. Recent specimen collections, including the first adult specimen from the Cordillera Central, establish plumage differences between populations of R. rabori in the Cordillera Central and Sierra Madre and reveal a third diagnosable population within Luzon. These differences have gone unnoticed because R. rabori (sensu stricto) had been known only from the juvenile holotype. Molecular phylogenetic data further support the hypothesis that three highly divergent taxa occur across the Luzon Island complex: Robsonius rabori is known only from the northern Cordillera Central in Ilocos Norte; an undescribed taxon (formerly included in R. rabori) occurs in the northern Sierra Madre in Cagayan, Isabela, Aurora, and Nueva Vizcaya provinces; and R. sorsogonensis occurs in southern Luzon (Bulacan and Laguna provinces), the Bicol Peninsula, and on Catanduanes Island. The existence of three putatively allopatric species within the Luzon island complex highlights the role of in situ diversification in island systems, and brings attention to the need for forest conservation to protect geographically restricted populations throughout the Luzon Island complex.
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Sorsogon Ground-Warbler Robsonius sorsogonensis (top)
Sierra Madre Ground-Warbler Robsonius thompsoni (middle)
Cordilleran Ground-Warbler Robsonius rabori (lower) |
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| female Sierra Madre Ground-Warbler Robsonius thompsoni |
Sierra Madre Ground-Warbler
Robsonius thompsoni Hosner, Boggess, Alviola, Sánchez-González, Oliveros, Urriza & Moyle 2013
'Ventriloquist' bird discovered in Philippines
— Birds are subjects of great interest to many people. They are often easy-to-spot, charismatic and beautiful. Because of this interest, birds tend to be well-studied, and most years see only a handful of new bird species discovered and described in scientific journals.
However, this past year has seen 23 new birds described so far.
Remarkably, three of those new birds have been introduced to science by researchers at the University of Kansas’ Biodiversity Institute. And a KU graduate student in ecology and evolutionary biology, Pete Hosner, has co-authored two of those.
“I think these discoveries reflect the opportunities I’ve had to work in tropical forests, where most new bird species are found,” said Hosner. “Since I began my doctorate in 2007, KU ornithology has had active field research in Central and South America, Africa, Asia, Australia and Oceania. Even though undescribed bird species are a rare find, with such a broad search radius, new things are bound to turn up.”
The KU researcher’s most recent find is dubbed the Sierra Madre Ground-Warbler, a ground-dwelling forest bird that lives on Luzon Island of the Philippine archipelago. Its description is published in the August issue of The Condor, a scientific journal of the Cooper Ornithological Society.
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| juvenile Sierra Madre Ground-Warbler Robsonius thompsoni |
“The ground-warblers are very unique birds,” said Hosner. “They’re only known from the northern Philippines, and they have no close relatives. As the name suggests, they’re ground-walking songbirds — rotund, with strong legs and weak wings — 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.”
Hosner said the new species of ground-warbler looks similar to the other two species of ground-warblers in the Philippines, 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,” he 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. The DNA sequence data was collected in KU Biodiversity Institute’s Molecular Phylogenetics Laboratory, which was recently renovated with investment from the National Science Foundation, the state of Kansas and KU.
“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,” Hosner said. “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."
However, it was the basic legwork of searching in the field for new birds that ultimately brought the Sierra Madre Ground-Warbler to the attention of the world.
“Most of the authors participated in fieldwork in the Philippines,” Hosner said. “Working in the Philippines is awesome. We hike out into the forests and establish field camps — usually about two weeks per site —where we survey the birds and other organisms. No electricity, no road noise, just the forest. Usually it’s hot, sweaty and dirty work, but we always camp near a stream for a water source, which helps. Sometimes our visits coincide with typhoons, which adds some excitement, especially when you are trying to keep your tent dry. One of the sites where we found the Sierra Madre Ground-Warbler, Mount Cagua, is an active volcano with thermal vents and mud pots.”
The new bird species’ scientific name honors Max Thompson, a retired professor from Southwestern College in Winfield and a research associate in the KU Biodiversity Institute.
“He received his master’s degree from KU in the '60s for his studies on the birds of Borneo, and he has conducted avian research on every continent,” Hosner said. “When Max retired a few years ago, his extensive research collection came to the KU Biodiversity Institute. We wanted to name the bird after Max for his decades of avian research around the world and thank him for his contributions to KU ornithology.”
Hosner’s co-authors are Nikki C. Boggess, Carl H. Oliveros and Robert G. Moyle from KU’s Biodiversity Institute and Department of Ecology and Evolutionary Biology; Luis Sanchez-Gonzalez from KU’s Biodiversity Institute and the Universidad Nacional Autónoma de Mexico; Phillip Alviola from the University of the Philippines Los Baños; and Rolly Urriza from the Philippine National Museum.
A five-year Biotic Surveys and Inventories Grant from the National Science Foundation, headed by KU herpetologist Rafe Brown, funded the field research. As of this year, the grant has funded 22 expeditions to the Philippines, and data collected on these expeditions has contributed to more than 120 scientific publications.
Peter A. Hosner, Nikki C. Boggess, Phillip Alviola, Luis A. Sánchez-González, Carl H. Oliveros, Rolly Urriza and Robert G. Moyle. 2013. Phylogeography of the
Robsonius Ground-Warblers (Passeriformes: Locustellidae) Reveals an Undescribed Species from Northeastern Luzon, Philippines
(La Filogeografía de Robsonius (Passeriformes: Locustellidae) Revela una Especie No Descripta del Noreste de Luzón, Filipinas). The Condor. 115 (3); 630-639 DOI:
10.1525/cond.2013.120124
