Per Bill D: Note the undertail pattern is black with a narrow white bar terminally and near the coverts. A Sharpie has light and dark bars with the light slightly wider, and the tail is overall light underneath. Another useful mark is the relative length of the wings and tail which on this bird are almost the same, the wings being a little shorter. In accipiters, the tail is much longer than the wings. Finally, note there is a faint teardrop pattern on the face, distinct in most falcons but relatively subtle on Merlins.