VICKSBURG, MISS. — A new species of Phylloscopus warbler — the Limestone Leaf Warbler (Phylloscopus calciatilis) — has been described from Southeast Asia: Description of a new species of Phylloscopus warbler from Vietnam and Laos (Alström et al. 2010) (hat tip John Boyd and Denis Lepage).
Update: Photos here and here.
The Limestone Leaf Warbler lives in karst forest in northern Vietnam and northern and central Laos and, the authors suggest, perhaps also in southern China. Earlier this year, the bizarre Bare-faced Bulbul (Pycnonotus hualon) was also described from karst habitat in central Laos. In the last 15 years, unique mammals have been discovered in the region as well.
The Limestone Leaf Warbler was known previously to science but apparently had not been studied in depth. It had been lumped with the similar Sulphur-breasted Warbler (Phylloscopus ricketti), which breeds in China and winters in Southeast Asia. For example, Robson’s Birds of Southeast Asia (2005) includes the following description in the Sulphur-breasted Warbler account: “Adult [resident] population (C Laos, C Annam): Perhaps paler yellow, greyer above, narrower crown stripe, slightly bigger bill. … Residents give quicker, slower-ended [song].”
In the abstract of the new paper, Alström et al. state:
In morphology, the new species is very similar to Sulphur-breasted Warbler Phylloscopus ricketti, but it is smaller with a proportionately larger bill and rounder wing. Its song and calls are diagnostic. Based on mitochondrial and nuclear DNA, the new species is most closely related to P. ricketti and Yellow-vented Warbler Phylloscopus cantator, and it is inferred to be sister to the latter. The mitochondrial divergences between these three species are at the low end of the variation found in other species of Phylloscopus and Seicercus warblers, but greater than in other taxa generally treated as subspecies. Possible introgressive hybridization between the new species and P. ricketti is discussed, but more data are needed to establish whether it does occur and, if it does, to what extent.
Phylloscopus is a fairly large genus of “Old World warblers” (for an explanation of the scare quotes, see here). The 60-odd species are small yellowish or greenish birds, many of which are easily confused with one another, though many have distinctive songs and calls. (North American readers, think empids.) They are widely distributed through Europe, Africa, Asia, and out as far as New Guinea.
Only one species, the Arctic Warbler (Phylloscopus borealis), occurs regularly in North America, where it is a summer breeding resident in Alaska. I have seen this species, not in Alaska, but on its wintering grounds in the Philippines.
Karst refers to landscapes formed when mildly acidic water eats away at an easily dissolved rock like limestone (a chemical process, not just a mechanical erosion process). This can result in rugged and spectacular formations, including steep mountains, caves, losing streams, and sinkholes. Karst formations are biodiversity hotspots all over the world, not just in Southeast Asia; for example, the blind, unpigmented Ozark Cavefish and other species are endemic to underground karst formations in the Ozarks of Arkansas, Missouri, and Oklahoma.
Because the Limestone Leaf Warbler it isn’t as weird, unique, or sexy as the Bare-faced Bulbul, it isn’t likely to receive similar global media attention, but it is one further indication of the biodiversity harbored in the karst regions of Vietnam and Laos.
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