not to microscopically dissect this or anything ... *BUT* ... a very soft, almost tree yelp - even when the birds are on the ground - has been a super killer call in my bag over the years ... i try to yelp so softly it barely makes a sound, and i restrict it to 3 notes (or less) ... there's a time & place for loud/aggressive stuff - but a very soft yelp has worked like a champ for me ... i do agree that the soft clucks & purrs are also money ... i've spooked birds & "purred" them back to me a bunch of times ...