I live in northern NJ and we have several hawks that use our property (and the surrounding forest and wetlands) as hunting grounds. We are getting our first chicken flock in Spring, so we have been watching them for the past year to see how they behave. One of the hawks that we have is a Harrier. It is a large (almost 2 feet tall) hawk and we have seen it take full grown rabbits. It often cannot carry the full weight so it will eat until the prey is light enough to carry or will tear it into manageable parts. They are ruthless when they attack. We also have Cooper's, Sharp-shinned, Bald eagles, and Red-tailed. I am sure we have some others as well. Last summer we had the local raptor rescue come to take away a great-horned owl that was roosting on the ground (ill). So we know we have owls as well. We fear for our little fuzzies that are coming, but we will have a covered run (not sure what will happen when we free range). I will let everyone know what happens when our chickens move outside.
We have noticed most activity in the early am and early evening (as have some other posters). Some of them will take a bird in flight (seems they particularly like the mourning doves). I ran one off after it had killed a bunny (just to see what it would do and to see how much damage it did with one hit). The bunny's neck was nearly severed at the base of the skull and the hawk just flew off and stared me down (from about 20 feet away). As soon as I moved off it returned to eat the bunny and carry off the leftovers. I am not sure if we can introduce any legal aversion therapy outside of having a presence when they are free ranging. I do know they are afaid of our dog. They don't come anywhere on the property when he is outside and they fly off if they see him.
Ther is a great site for wild bird identification that includes markings, habitat, call audio files, pics, and videos. I hope it helps you identify your babies tormentor (not that you can really do anything since they are protected):search for allaboutbirds or the Cornell Ornithology Lab Bird Guide (I cannot post the link because I am a newegg).