What is that sound!

[jackandkaren]

My new chicks are spending some time getting to see my older hens and one of my older gals is making a new noise. Very low pitched. Is this meant to be threatening or reassuring. I've never heard her do it before! [youtube]

[youtube/]

 

[Kiki]

LOL..she is probably telling them a not so nice story??
I've never heard this. It's cute.