EUROPEAN ROBIN: Why does it sing at night? 

The sweet and prolonged singing of the European Robin can be heard during the night-time, when the noise of the city dies down. Do the city lights wake him up?
(Every Friday in just 1 minute ...naturally!)
Note: For more information, the works are recommended:
Fuller, R.A., P.H. Warren, P.H. & Gaston, K.J. (2007). daytime noise predicts nocturnal singing in urban robins.Biology Letters 3, 368-370
Cuadrado, Mariano (1997). Why are migrant Robins (Erithacus rubecula) territorial in winter: the importance of the anti-predatory behaviour Ethology Ecology & Evolution, 9:1, 77-88