34.5 - 37 cm. 91 - 95 cm wingspan. 330 g. Median size. Wings long, fairly narrow and pointed. Males and females are similar. Dark plumage: Blackish brown overall, with indistinct M pattern visible above in bright light. Underwings show dull silvery flash across base of outer flight feathers. Rarely the coverts of the outer flight feathers show a bright whitish flash and whitish crescent. Paler dark morphs have paler brownish underbody; a whitish mottling on outer feathers that cover underwings. Legs black. Clear plumage: Head and chest pale brownish with a white patch on throat. Underparts white. Upperparts gray-brown to brown, with indistinct dark M. Underwings with brighter white flash at base of outer flight feathers and whiter mottling on outer coverts than dark morph. Legs black and flesh. Juveniles are similar to adults.