There is a new study from Nature which looks at why after a lot of secretive behaviour in order to deposit their eggs into a hosts nest they give a "conspicuous ‘chuckle’ call". (I kind of think of it as an evil laugh with thunder and lightning but this isn't in the paper)
They find that this distracts the mother reed warbler in a similar way as if it were the call of a sparrow hawk - which is not seen with male cuckoo calls or collared doves. This they further argue leads to a greater uptake of foreign eggs because in these cases the warbler is more worried about their own safety than that of the clutch.
I can't say I know a lot about Cuckoos other than clocks but I guess there might be other interesting things knocking about. Also as they are parasitic in nature may link to some of the "P" series stuff.
Thanks for reading this and hope that it is useful / provides something to think about :)