Hello Englishmen! I'm very glad to see that this topic is being discussed somewhere in the world.
        I'm a Dane, living in Jutland. I've tried in vain to get information in Denmark about the cuckoo interval. I have observed that the Danish cuckoos most often sing a diminished third, as is to be heard in F. Delius'orchestral music "On hearing the first Cuckoo in Spring" or as the two first notes in "When Johnny comes marching home" or in "The keeper would a-hunting go". But this spring I have once very clearly heard a cuckoo singing again and again a quarter – as the two first notes in "Hey ho, nobody home" or the two first words "We'll take (a cup of kindness yet)"in the last line of Robert Burns' song.
        Can it be true that there is no printed matter to be read about these varieties and whether they are dependant on heredity or time af day/year or weather or geography or something else?
        Please excuse my poor English. I hope it's understandable.