Well this was timely: https://soundapproach.co.uk/which-c...Ua8zu-TOZ0wxxq6hVoPrixAvmcVQLZE7HBGl26jyxLEBc
About the leiern song, Blackcaps in Italy, especially in the south, do this all the time, with the occasional bird sounding very similar to Western Orphean (which contrary to most field guide maps, is nearly extinct in Italy as a breeder)
As you say, Cajanuma: how timely was this piece indeed! It almost feels like I've delegated this work out to the Cosmos and let somebody else do the work for me!
As to the leiern motifs...well, I couldn't condense what BWP has to say without losing some of the meaning in translation, so I've just copied it and included it below. I assume Mark C must have read it at some point? But if he hasn't, or he's forgotten about it, I think its fair to say that his attempts to make any kind of sense about the variation in Blackcap song in southern Europe must belong in the category of wishful thinking?