I recently read this article and was wondering whether mixed singing can interfere with nightingale identification based on song? There where I live common nightingales seem to far outnumber thrush nightingales. The benchmark for their discrimination is supposedly the presence of a series of low, sweet whistles (I would say it should also end with a jumbled flourish, but I'm not sure if it's official). My experience with thrush nightingales is purely anecdotal, but they seem to be able to produce these whistles, too, albeit no more than two in a row and with no flourish at the end of the phrase. I suppose there are also other differences between the birds' songs (pace, liquidness), but I'd prefer to stick to the hard-and-fast.