According to new research, it appears that British robins have switched to singing at night when in urban environments, in order to be heard:
“There are two ways of looking at these results,” says Fuller, who admits he does not know if the birds that sing at night are vocal in the daytime too. “On one hand, you could conclude that these birds are highly adaptable to the urban environment. On the other, it could be that they are suffering from the poor-quality habitat and having trouble attracting a mate.”
I live in Birmingham, Alabama, and have noticed this summer that the birds are singing at night. I do not think it is a mockingbird, but several birds, but have not gone out to listen closely. They sing loud enough for me to hear them and I have noticed them all summer. I live on a beltway so there is considerable noise all night long.
Nice observation! Does it seem that there are more or less birds in general in the neighborhood? If less, it might be indicative of the birds having trouble finding mates.