FIELD MARKS-Black-throated Blue Warbler male is dark blue on head and upperparts, with black face, throat, sides of the breast and flanks, contrasting with gleaming white centre of breast and lower underparts and conspicuous white patch at base of primaries. It has conspicuous white patches in outer tail. Legs are black. Eyes are black. Bill is short, thin and black. --Female has a rather dull dark greyish-olive green above and buffy-yellow below with conspicuous whitish surpercilium, a broken whitish eye ring, and a whitish patch at base of primaries. Immature is similar to adult. Back and head feathers of male are edged with green, undersides are tinged yellow, and has some white tips to black feathers on throat.