What bird is this? [audio]

I hear this thing around my backyard all the time, finally managed to get it on audio today (video actually, but the bird never made an appearance, so I just extracted the audio). It shut up and stayed invisible in the tree shortly after I moved out into the yard.

~14 seconds, 220KB: http://75.65.123.78/mysterybird-8-20-14.mp3

I have seen them way up high and making these calls, circling in thermals but too far off to ID, they are very large birds...

I would guess a hawk of some kind .

Well captured!

Certainly not something that I have ever heard over here :-)

Maybe, a Red-tailed Hawk. Some type of hawk.

Here's a good site for listening to many birds and the link is for ACCIPITRIFORMES

The main site is here.

In NJ, we have a lot of mockingbirds. The sound is always a mockingbird there. I have no clue what bird yours is, but your geographical location would help identify.

Sounds most like Harris's hawk, but I'm in the wrong part of the country - east central Mississippi. Or these birds are very very lost!

So you.re close to the flyway and birds are already migrating early this year. I’ve seen many species leave already here. Possibly migrating hawks of some kind. Have they been here all year or are they new to the area?

I have heard the calls most days since early spring. Not necessarily the same birds the whole time of course, but that's too long a span for 'just passing through'.