Blackbirds are my favourite songbirds when it comes to listening to birds. Yes, Nightingales are impressive but they lack the composure and serene delivery of the Blackbird. Of course this is a purely human way of sensing this aural signal and it is interpreted in a very different way by the birds themselves, particularly neighbouring males in competition for territory and potential mates. I made some recordings this evening of a Blackbird singing at dusk in Sunny Hill Park, London, c10 metre up in a tree top. This has been its favoured song post for some weeks now. This individual averaged around 9 phrases/minute each lasting 1.5-2.5 seconds with a 5 second pause between each as illustrated in the figure below. The second figure illustrates some of the unique phrases in a varied repertoire from the same individual. Each phrase consists of slow frequency modulated pure tones between 1.5 and 3.0 kHz, often followed by a more complex and higher-pitched flourish.
Larger versions can be viewed here: www.fssbirding.org.uk/blackbirdsonogram.htm