unknown raptor

This morning perched on the dead tree my end - size- about 40 cm; colour: very dark all over, nor specific head markings, front seemed rather mottled dark and light grey, type - I's say falcon; - I was about 50 meters or so away, not a long look, the bird was harassed by another small bird so flew off, glided liesurely pace down at tree-top height - maybe brown falcon?; none of the usual raptors sighted here. 9.00 am 28-2-2009