Thanks Stuart, a few other features of this bird that favour Brown over Black include the lack of feathers on the legs (seen in pic 1) - Black Falcons have more extensive feathers down to the feet. Brown Falcons also have a more upswept, bent wing shape in flight, like pic 3, whereas Black's typically fly on flatter, slightly bowed wings. The facial markings are not always the most reliable feature, especially since they are fairly variable, some Browns are less evident (e.g. this bird), and some Black's, particularly worn birds, can show some teardrop-like markings on the face.