I believe he has already 'done' singing with nightingales.

Maybe he should take his pilgrims to somewhere where larks might be singing - there are several songs about larks, and he could play them a recording of Vaughan Williams's 'Lark Ascending'.

And he does seem to like the idea of communing with his chosen birds, so perhaps he could go to a free range chicken farm and crouch in the hen house singing 'Ain't Nobody Here but Us Chickens'.