Okay, we’re gonna nail this vocalisation thing. We understand that language is a poor instrument to describe colours and sounds. So, let’s use process of elimination. Let’s go nibble by nibble: ‘O k a y – yes, I know that sound!!’ So, if you agree with a claim, be so kind as to post: ‘Yup!’ or ‘Nuh!’ One: chicks peep: ‘Yup’ or ‘Nuh.’ Two: only females ‘boom.’ ‘Yup’ or ‘Nup’? What is a boom? I ruckon it’s what the bird in this photo is doing, an unmistakeably deep and repetitive sound. (So, all calls that are not ‘archetypal’ – that is, clearly recognised by all players – shall be considered later.) [Something I am privileged to see is the 'marking of territory' by females during breeding-season. You read that a female's boom can be heard a long way away. Correct!! I did the first round of this research last winter. I was astounded when I realised what was going on, that is, the first time I heard a distant female reply. My position is: 'booming' is defined by (a) the 'string'of booms, between a dozen and twenty, and (b) the bass of the booms. Both Felicity and Greedy did it, to two local females (South West Female and North East Female) on different days, while I watched from this distance -- 'booming'!!) S.E.