By Matt Walker
Editor, Earth News
A Limestone leaf warbler caught at Thai An Commune, Quan Ba district, Ha Giang Province, East Tonkin, Vietnam on 1 June 2008
A new species of warbler has been discovered in the forests of Vietnam and Laos.
The small green and yellow bird was first sighted in 1994, but at the time was thought to be a different species surviving 1000km from its usual home.
Now studies of the bird's morphology, DNA and vocalisations have confirmed it to be a unique species. Scientists have named it the Limestone leaf warbler.
Details of the bird's discovery are published in the journal Ibis.
"The bird was first seen at one place in Vietnam in July 1994 and again at the same place in April the following year, and in one area in central Laos in May 1995," says taxonomist Professor Per Alstrom of the Swedish Species Information Centre, a part of the Swedish University of Agricultural Sciences in Uppsala.
"Initially, the bird was identified as a Sulphur-breasted warbler, in itself an interesting finding, since it was apparently breeding more than 1000km south of its previously known breeding areas in China.
"Later it was realised that its songs differed markedly from the songs of the Sulphur-breasted warbler, and further studies were undertaken."
These studies by Prof Alstrom and colleagues, who included scientists from the Wildlife Conservation Society's Lao Program and Birdlife International in Indochina, confirmed the bird's unique identity.
The plumage of the Limestone leaf warbler (Phylloscopus calciatilis) is almost identical to that of the Sulphur-breasted warbler (Phylloscopus ricketti), though the new species appears to have a colder yellow chest and more grey topside and stripped crown.
But the new species is smaller, with shorter wings, rounder wing tips and a proportionately larger bill.
"Its vocalisations, both song and contact call, are markedly different from those of the Sulphur-breasted warbler," says Professor Alstrom.
DNA analyses also suggest that it is more closely related to the Yellow-vented warbler (Phylloscopus cantator) from eastern Himalayas, northern Laos and adjacent part of China, which is quite different in plumage.
In the past two decades, 19 new species of Phylloscopus warbler have been identified
Many warblers look similar but have very different DNA
Each species of warbler may produce very distinct songs
So the new species looks markedly different to its closest relative, Professor Alstrom explains, but very similar to its more distant relative.
"The most likely explanation [for this]," he says, "is that the plumages have not diverged much in the Sulphur-breasted and Limestone warblers since they separated from a common ancestor."
Surprisingly, the Yellow-vented warbler and the Limestone leaf warbler separated from a common ancestor much later, but have diverged much more in plumage.
The vocalisations have similarly diverged in all three species.
"Leaf warblers and many other warblers are renowned for being very similar-looking, while having distinct vocalisations, so it is very likely that other new species of warblers will be discovered," says Professor Alstrom.
Despite being unknown to science as a new species until now, the Limestone leaf warbler is quite numerous.
Professor Alstrom's team believes that the bird inhabits limestone karst habitats in Vietnam and Laos, and may also breed in several locations in southern China.
One other new species, the Bare-faced bulbul (Pycnonotus hualon), was described earlier this year from central Laos. Its habitat is similar to the Limestone leaf warbler, which highlights the ecological importance of the region.