That is odd that they would attack your birds. I know they will go after a distressed critter but they do not normally prey on a live healthy animal. They are mostly scavengers.Turkey vultures tried to get my younger Delawares some years back. Several vultures chased and caught up with one pullet. My dog and I heard the noise and ran outside, chased them away. She was bitten and scratched up, and lost a lot of feathers. Doc gave her antibiotics and a vitamin shot and we kept her in a crate on her own until she healed up. She lived to eight years old, had a scar on her back and a slight limp the rest of her life. But she was a good layer!
Now I don't let the young ones or bantams free range unless one of the dogs or the geese are out. When I see the vultures swoop low over the yard (probably to see if anyone is available), I yell and wave my hat at them. The chickens and ducks and geese seem to appreciate that!