magnirostris is not a subsp. of Buteo nitidus. Probably ssp. pallidus.
Yes, this was a slip; I am sure that the previous clip uploaded that day was a Roadside Hawk, and hence the name magnirostris. Anyway, my reading of the subspecies ranges of the Grey Hawk makes me thing that in this clearly Amazonian locality, as well as in Cristalino, were you took pictures, the subspecies is more likely to be the nominate rather than pallidus, which it sounds to me as occurring south of Amazon. I leave the subspecies blank, meanwhile, but if you have more information to clarify this I would be very happy to know.