We have had several robins at a time in the small front garden area where we have our bird feeders. With robins being very territorial, even at this time of year, this has led to quite a bit of conflict. As well as singing, robins use quite a lot of different threat displays, including puffing their redbreasts out, head-swaying and ultimately physical attack. Usually one bird or another is chased from the scene.
Interestingly I’ve been hearing robins singing at unusual times – eleven o’clock at night and four in the morning, for example. A sign of bright security or street lighting fooling the birds into thinking that it’s daytime, perhaps?