Limestone Leaf Warbler Phylloscopus calciatilis is presumed to breed in Guangxi and Yunnan near border with Vietnam; known to breed in northern and central Vietnam and northern and central Laos. Discovered 1994 in forests in rugged limestone karst region of Vietnam. Initially considered disjunct population of Sulphur-breasted Warbler P. ricketti; described as new species in 2009. Plumage virtually identical to Sulphur-breasted Warbler. Distinguished with difficulty by slightly smaller size, proportionally larger bill, and rounder wing (shorter primary projection). Songs markedly different: Both species utter series of quick, high-pitched, slightly descending phrases, sit-SIT-see SIT-sit soo-SA-chew, with Limestone Leaf being clearer and more slow-ending and deliberate and Sulphur-breasted ending in a slurry trill. Double-note call similar to Yellow-vented Warbler P. cantator but even more emphasis on last, lower-pitched syllable. — Craig Brelsford
Daniel Bengtsson served as chief ornithological consultant for Craig Brelsford’s Photographic Field Guide to the Birds of China, from which this species description is drawn.