Small leaf warbler with vivid yellow underparts and greenish upperparts. Readily distinguished from most other leaf warblers in range by bright coloration; Hartert’s can be similar but has a weaker brow pattern, is paler yellow on the underparts, and has a habit of shaking its wings--a habit lacking in Sulphur-breasted. Breeds in mixed hill forests but can turn up in a variety of wooded habitats on migration. Song is a series of bright, high-pitched accelerating notes. Call is a bright “pi-pew.”