Ok, I found my copy of "The Sounds of Star Wars":

An interim crow sound was tried before Burtt arrived and recorded Wood and Acord in the parking lot behind the Tech Building. "He sourced from Dave and me yelling" Wood says. "We screamed and screamed. I was trying to model mine off this terrible, cheesy element that I love from a Disneyland ride, The Haunted Mansion: ah, ah, ahooooooah!"

Utimately, Burtt blended the screams -with Acord starting the scream and Wood ending the scream. "It sounds like some kind of weird animal but coming from a human" says Wood