A small bird of lowland and montane forest and edge. Unmistakable; the only nuthatch in its range. Blue above with a black edge to the wing, a black forehead, a thin black stripe behind the eye, pale pink underparts, and a yellow bill, eye, and eye-ring. Often joins mixed-species flocks. The only woodpecker similar in size is Philippine Woodpecker, but Sulphur-billed Nuthatch is blue rather than brown. Voice includes high-pitched, descending shrieking calls and sharp staccato chips.