Limestone Leaf Warbler

The limestone leaf warbler is a small Phylloscopus described as a distinct species in 2009 after birds first noticed in Vietnam in 1994 had been mistaken for Sulphur-breasted Warbler. Its plumage is nearly identical, but it averages smaller, with rounder wings, a proportionately larger bill, slightly colder yellow below and greyer upperparts. Voice is the most reliable field distinction between the two (Alström et al. 2010; Shanghai Birding).

This warbler is strongly associated with broadleaved evergreen and semi-evergreen forest on rugged limestone karst in northern and central Vietnam and Laos, with occurrence also reported in southern China. Vietnamese observations span low karst at Phong Nha-Ke Bang to well-vegetated slopes around 1,200 metres in Ha Giang. It forages through forest foliage for small invertebrates, using mature forest, secondary forest and, locally, tall secondary scrub where these remain on limestone (Alström et al. 2010; Wikipedia habitat summary).