Why not a juvenile Sharp-shinned Hawk?
Not a 1st year Sharpie for a few reasons: bad Accipiter structure in general, not long enough tail, very pale undertail, and the tip of the tail is DARK vs. light.
NOTE: J. Moore - glad to see you come to the RSH side - now just for the sake of documentation (and the fact that I already wrote this long post and don't want it to go to waste, hahaha) here are my responses to some of your points:
To me, the legs are too thin, and the chest too narrow relative to the head, to be a buteo...
Narrow chest and thin legs like this?
http://www.birdforum.net/gallery/showphoto.php?photo=178022
...I am hesitant about red shouldered because of plumage characteristics, e.g. the light throat and face and the fact that thin tail bands are not visible. See this photo of an immature red shouldered for example, which has a dark throat and visible narrow tail bands even when seen from underneath:
http://www.ascabird.org/redshd_herron.jpg
Variability, ma brotha. You can show me a million photos of dark throated, prominent tail-banded young Red-shoulders, but the fact is I can throw back a good number with light throats and less prominent tail-bands. See 1st attached photo to start ("Red-shouldered Hawk, immature" - source: BNA "Appearance" section of RSH).
Plus, if you're saying that the undertail is too PALE for Red-shoulder, then I don't know where your Merlin argument stands considering that Merlins of all ages and North American races have exTREMEly dark undertails. Under Merlin's "Distinguishing Characteristics" section of the BNA site, it's stated: "The
dark tail with 2–5 highly contrasting narrow light bands helps distinguish the Merlin..."
The eye should be dark in a Merlin
Also, in some hawks (not sure about Merlin), immatures can have different eyecolor than adults.
I don't know too much about aging Merlins, but doing some skimming through BNA info and BirdForum photos, all evidence points towards juvenile Merlins having fully dark eyes like adult Merlins:
See 2nd attached photo ("Juvenile Merlin, boreal subspecies (columbarius), Cape May Point, New Jersey, October 2002." - source: BNA "Distinguishing Characteristics" section of Merlin)
http://www.birdforum.net/gallery/showphoto.php?photo=118283
http://www.birdforum.net/gallery/showphoto.php?photo=42734
When was the picture taken? If in summer, could this maybe be a juvenile Broad-winged Hawk? Here is a picture that makes me think this:
http://content.ornith.cornell.edu/UEWebApp/images/KTK_112002_100005_L_1.jpg
The mystery bird is less heavily streaked, but the features looked similar to a Broad-winged to me.
Linda
EDIT: Okay so Dick just clarified it was taken last summer.
As far as Broad-winged, I feel iffy about it, and I'll come back to analyze further later - I have to jet to class right now (Bio class, coincidentally). I will just quickly note that I believe young Broad-wings have dark (or at least darker) eyes than young Red-shoulders. See 3rd attached photo ("Broad-winged Hawk, juvenile in-hand." - source: BNA "Appearance" section of BWH).