I'm going to say "Cooper's"

I went for a photo walk this morning; there's a lot of flowers in people's front gardens this time of year, and the weather (severe thunderstorms expected after noon) didn't seem sensible for a bike ride.

So I got to have this flash of avian motion go by in the corner of my eye, and the slow "that's not a robin" thought, and then the glimpse of strongly barred tail that connected to "it can't be a hoopoe" which is at least evidence that the most recent bird image I happened to have looked at stuck.

There were four obviously juvenile accipters; I presume a successful clutch.  (The tree is in a small park adjacent to a primary school; it looks very wild but I was standing on asphalt and there were half-a-dozen children and parents on their way to school looking up around me.)  I only got pictures of one; I'm rather pleased with myself that I managed to get the macro lens swapped off for the long zoom in an expeditious fashion, since there was a fair bit of in-the-trees movement going on.

At the time, I thought they were Sharp-shinned; they didn't seem much larger than robins.  Then I got home and looked at the better pictures.

juvenile Cooper's Hawk in a conifer

I'm chewing my way through Peter Dunne's Essential Field Guide Companion which makes the point that Sharp-shinned hawks can't turn their heads like this.  (They have to drop a shoulder.)  I recall a discussion at a TOC meeting where Mark Peck of the ROM pointed out that Sharp-Shinned has much larger and distinct "raindrop" streaking on the breast.  (Which makes me doubt about this one.)

On the other hand

same juvenile Cooper's Hawk, same conifer, less obscuring foliage

Those are neither especially spindly legs nor a narrow white terminal tail band, and there's russet on the head and nape.  So I'm going to say it's Cooper's.