Hook-billed Kite: beautiful adult black morph series of flight shots
This black morph (referred to as dark morph by Wheeler) shows a blackish head, upperparts, and underparts including undertail coverts that are field marks for this color morph. [notice the bird is going over a power line in two photos and under a power line in next photo--the bird was going through a multiple lines]
This bird also has a white iris that is found on adult birds of this species.
Determining gender is a little more difficult. In Raptors of Western North America Wheeler notes that male dark morph's have 'uniformly black' remiges on the underside of the wings. He notes that females may also have 'uniformly black' undersides of remiges but may also "...one or more primaries have large, irregular white spotting." (p. 79)
Though on a couple of these photos there are possible whitish areas on the undersides of it's remiges, but these could just be just photo irregularities (due to lighting, missing feathers, etc).
Wheeler in Raptors of Western North America states that the tail of an adult male dark morph bird has, "One broad all-white band on the mid-section of both dorsal and ventral surfaces." (p. 79) Wheeler states that females also have a broad white mid-tail band plus a ". . . second narrow white band on the very basal region may show on the ventral side if the tail is widely fanned when soaring." (p. 79)
I think this may be a female because there is some white showing on the ventral side of the base of this bird's tail in the 2nd and 4th photos on this page when photos enlarged. SeEtta