We've had Red Tails in abundance for quite a while and most recently noticed a young bald eagle. The Red Tails regularly take rabbits and small rodents from around our yard (a couple of acres of open ground pretty well surrounded by old growth hardwoods). Our hawks will find a nice high limb to sit on and the only way we notice them is when they pounce, or when other birds give warning. Robins have a very distinctive warning cry for example, but of course that only matters if you are outside too. There is also an owl in the nearby woods, but we don't know the type beyond HUGE. We also have noticed a total disappearance of rat burrows that used to constantly appear near compost and wood piles, so you kind'a learn to take the good with the bad.
I trust ravens even less than hawks, and they are a lot smarter than other birds. They are the racoons of the bird world, and will study things to figure out how to attack. I have no personal experience with them and chickens, but anything that can take out a hawk is never gonna make me feel safe about them being around my chickens. The crows are a pain in many other ways, so I would tend to avoid encouraging them as well. I've seen the eagle take a huge rabbit right on our neighbors lawn, and he didn't seem the least bit interested in flying away to eat his score, even though it was well within his capability. Much to the dismay of the little girls, and the delight of the little boys, in the vicinity, he was happy just sitting in the middle of the lawn and shredding the rabbit while everyone stood at a distance and watched. I would say that the individual animals are adapting to their dwindling habitat by getting more comfortable or bold in their interactions around humans. This is certainly true with our deer from the adjacent State park, that has only very limited hunts, and is grossly over populated. You could literally walk up and club these deer with a hammer they are so used to being around humans.
A friend a few miles down the road has had hawks attack his run cover while he was in the run, so I would have to repeat the obvious refrain - nothing short of a covered run, and a well covered one at that, is fail safe. Ours is 30'x40' and my roof is cattle panels tied end to end and tensioned by the two outside post 2x6 runs that join them together. The two opposite lines of posts are tensioned and kept plumb to force an arch in the cattle panels by crossing side to side with four lines of s/s braided wire with turn buckles. I also have a 2x8 ridge beam under the panel joints and 17 ga. galvanized stucco wire over all of that. The sides are 8' tall to enclose a mini orchard of dwarfed fruit trees, and they get the same treatment. Just outside of that we're installing a 30" electric coon fence and maybe a few more wires on the run itself. Anything worth doin' is worth over doin' right?