My roo is a screaming banchee!

I got my first roo about 2 weeks ago. He is in quarantine now but occasionally can see the girls when they are free ranging. Sometimes he does this horrible shrill scream, usually when they take off in a pack together or something like that.

Does anyone know is he mad? Frustrated? Excited? All of the above? I never heard a roo scream like that before...

A little side note, we bonded tonight. I held him on my lap and after a couple minutes I let go of him and he stayed there, laid down while I pet him and fell asleep...he didn't get down for 20min!