Spectrogram of marsh warbler song(= Mastersingers, Marsh warbler 3). Sv: Kärrsångare. Hålanda, Sweden, midnight, mid-June 2011. Telinga Pro 5 parabole with stereo DAT mic. Sonogram from Izotope RX, screen capture with Debut v. 1.83. The recording is of 17 consecutive minutes so the file is big and may take time to load.
A passing airliner disturbs the silence between 1'30 and 4'30 but I chose not to use any noise filtering. It seems that the bird is not only singing, listen for example to the wing-clapping (?) at 3'49 and on.