i agree [with Sharpie], squared off tail
Be careful. "Squared-off tail" is a field mark that stems from relative length of rectrices (tail feathers), and can only be evaluated in flight, or maybe with an undertail glance. Coops' tails are said to be "rounded-off" because they have graduated rectrices, that is, the outer ones are shorter, giving a rounded like appearance in flight. Perched, however, these graduated feathers are hidden in the undertail and a view like this of the back of the tail can be misleading if the "squared-off" vs. "rounded-off" field mark isn't applied correctly.
That's a tough one!. But if I had to say one way or the other, my vote (FWIW) would be for female Sharpie, mainly because of the breast streaking.
It's a 1st year bird, and as far as I know there is no way to accurately sex it from this photo (besides perhaps size comparison in the field, which we have absolutely no grounds to evaluate seeing that there's nothing in the photo to compare it to).
Before I cast my vote, I want to post a general note about breast-streaking. I feel like it is being over-emphasized in this thread. Personally, I do not weigh it too much into my analysis, because both species are variable.
Here are some 1st year Sharpies with dark, thin breast-streaking (contrary to the "expected" light brown, tear-drop shaped streaks):
http://www.sdgfp.info/Wildlife/Diversity/birdbanding/images/other birds/sharpshin3.JPG (P.S. check out that great undertail view showing the equally lengthed rectrices)
http://www.birdforum.net/gallery/showphoto.php?photo=128277
http://adampaul.files.wordpress.com/2006/10/img_4540.jpg
http://canadabirdingphotography.com/wp-content/uploads/2007/11/dsc_6867.jpg (this is a great one)
http://www.birdforum.net/gallery/showphoto.php?photo=162814
And here are some 1st year Coops with lighter, wider breast-streaks (contrary to the "expected" thin, dark brown streaks):
http://www.birdforum.net/gallery/showphoto.php?photo=175307
http://www.birdforum.net/gallery/showphoto.php?photo=178072
http://www.birdforum.net/gallery/showphoto.php?photo=167779
http://www.birdforum.net/gallery/showphoto.php?photo=170780
http://farm2.static.flickr.com/1252/1475107132_bc2b42f1ab.jpg
http://www.themodernapprentice.com/coopers_immature.jpg
http://picasaweb.google.com/boehmester/FirstWeekOfJune/photo#5073835570300977666
http://www.ojaigarden.com/images/cooper-mama-web.jpg
Now, as for my vote. Initially I was thinking Sharpie. I glanced at the tarsi, they seemed thin, but things just weren't adding up. I went back to compare Coop and Sharpie tarsi in photos and felt turned around a bit - I've been away from both the site and birding in general for a while just because I've had so much going on this year, so I needed to refresh my Accipiter analysis.
So I reached the point where I found the tarsi on this bird to be acceptable for a Coop. We have some weird angles for the head, but I just can't seem to make it nice and rounded as I'd like on a Sharpie. Then there's the issue of the tail. Now Sputnik, I apologize in advance for pulling a 180 here from what I said earlier in my post. USUALLY the back view of an Accipiter tail is fruitless as far as determining if the rectrices are graduated or not. But in this second shot, I believe I see a shorter outer tail feather sticking out to the left (it's mostly tucked away in the undertail - see attached photo. EDIT: Scott, I just reread the thread and saw you noticed this too :t
.
I'm open to discussion on these issues (tarsi, head-shape, tail feather), but I feel good about Coop.