You have hawks that target crows? That's really rare. Crows are large, comparatively dangerous, highly intelligent prey, which mob hawks even more enthusiastically than most birds.
A vulture might circle your yard if it smells something interesting nearby, or if you have a thermal overhead.
Vultures are big! I've seen some fairly close up. Sometimes an animal gets killed on the road in front of our house, and I always move it out of the road so vultures trying to feed on...
Lambs are pretty helpless. They can't do much about corvids. Chickens run and flap and squawk, they're a lot of effort to get at. Either way, corvids predating on things their size or larger is fairly rare, it's too much effort. If you see an entire mob of them watching your chickens, you might...
Scarecrows won't work on hawks. Dogs might.
Vultures, which should largely be considered harmless, are largely black or dark grey. They have naked heads, and a hunched posture when perching. They're very slow and usually circle or glide. The feathers at the ends of their wings are spread apart...