I have 2 pairs of red tailed hawks nesting on my property. Crows definitely do not deter them well, I saw a murder of crows harassing the pair behind my coop for a few weeks but they soon gave up after they realized it was a waste of time and the Red tails did not care. I have not lost a chicken to a hawk for the past 2 years. We had a Cooper's hawk attack a small cockerel a few weeks ago and my 21 other roosters and cockerels did nothing, which disappointed me, luckily my brother was able to get out there and spook the hawk away. The most recent hawk attack besides that one was like last March, it was another Cooper's hawk and it tried to catch a duck. I had 5 ducks and they saw the hawk coming, instead of running they just sat up next to the wire on the run and squawked like crazy, the hawk was like 5 feet from them and then they all jumped out of the way and it almost hit the wire, he failed that attack and flew off.
I don't know why the Red tailed hawks never attack, they are supposed to be the number 1 chicken hawk. I think it is because they are scared to come down on a bird while there are so many dogs around. The coop is in between 2 dog kennels and there is a third dog kennel a little further back. We have 12 German Shepherds. My neighbors lost 3 hens in one day to Red Tailed hawks last March. Red Tailed hawks are my favorite raptor, I once saved one when I was a little kid. We were on a walk through our woods after a big storm and found a juvenile RT on the ground, we brought it back and kept it in the chicken coop, I fed him ground beef, moles, mice, and chipmunks. At the time I was not aware that it was illegal to keep a hawk, he did survive though and eventually left after he was confident with his hunting skills.
Btw, my chickens free range, unsupervised, from 6:00 am till 8:00 pm.