When a GSP wishes hard enough

Yesterday our GSP, Duke, and our beagle, Annie, were very fixated on the birds in the giant maple tree in our backyard. In the late afternoon, my husband took this picture of them hanging out together, staring upwards.

About ten minutes later, we heard a big, birdy kerfuffle high up in the tree, followed by a small thump on the ground right next to where the dogs were. Annie immediately leaped forward and grabbed something. Ted and I asked in tandem, is that a bird? After a moment Annie dropped it, and Duke grabbed it and started trotting proudly around the yard. Ted went to get something to put the probably dead bird in. When he got back, I got hold of Duke and pried his mouth open. What tumbled out was indeed a dead bird, but the interesting and horrifying thing was that it was decapitated. What could have done that? Definitely not a cat -- with four dogs running around, cats stay out of our yard. At that time of day, could it have been a hawk? Surely not an owl during the daytime.