43 cm. 180 g. Bill black. Crown black. Forehead white. Sides of head white. A black mask joins with the crown. Upperparts black. Throat and chest white. Belly and flanks grayish-white. Feathers that cover underwings white. Wings black. Tail forked, black with white border. Legs black. Non-breeding adult (September-January): Nape grayish. Breeding adult (January-September): Nape black. Upperparts deep black. Males and females are similar. Juveniles have the head, chest and upperparts sooty blackish brown, scaled with white on back; feathers that cover underwings white.