I have two possible 'roo' suspects, possibly three. I've caught two of them opening their beaks really wide and standing tall, but no sound comes out. Is this an attempt to crow? Its like they are doing a long burp but without any sound effects. I haven't seen the others do it so that is what made me think of the crowing but I guess they could just be stretching their mouths or something? Does anyone know what I mean and if this is a mini crow? 
