Hi Alexander
Thank you very much, very interesting proposition, I could never have though to Stone Curlew. It sounds so different to the 'classic' call I know! But if you say that they can have have a wide range of variation then, I trust you! Moreover, on XC, I found a record that could indeed match =)
As for Black Kite, that could be possible in terms of phenology, but I think they migrate mostly alone, and one that record, it sounds as if there were two birds... But why not =)
Does anybody else have some supposition?