Actually, I think Avian Scream needs to be maxed for it to happen(certaintly doesn't work at 1, or 2, but I know it works at 6. Haven't tested in between). Hardly anyone has it, but birds have the range that being stuck isn't a life-killing thing.
Another thing in the back of my mind was making HS have a much longer range, 10-12 instead of 8. The mini stun might help bears get closer.