They might like a scarecrow to perch on.
If a human moving about in the yard with the chickens doesn't deter a determined Hawk, I don't see how a stationary Scarecrow would be of benefit.
Hawks can see Black Chickens just as well as any other color. Tall weeds and bushes can make good cover, but Hawks sit in trees and observe their prey....for days, every day (study movements, times, habits).
They can land and just walk right under that bush, under that building/hiding place or wherever and attack (Yes, Hawks can walk). They are also very good at just taking a dive and driving their prey right into the ground with pinpoint accuracy.
When Hawk activity is high, the only assurance of deterring an attack is to keep birds penned in a secured area that a Hawk (or predator) can't get into. Anytime chickens are loose and roaming, there's a risk that a predator will take them or attack. Sorry, that's just the way it is.
Of course, this is only my personal firsthand experience when dealing with Hawks and other predators, so it's possible someone may offer something more positive.
