The European starling is definitely a good mimic. I grew up in England. When I was a child (in the days before everybody had digital alarm clocks) my brother would whistle to wake me up in the morning. A starling learned to imitate the whistle, and I kept getting up for school too early, as I could not tell when it was the bird and when it was my brother.
I can also attest to mockingbirds singing all night, as one used to perch on the roof of my house in PA and sing endlessly at all hours, the mad thing! There are no mockingbirds where I live now, but I'm told they are moving north and if Global Warming continues they will be here one day.
I've also been fooled by blue jays sounding like hawks, but I didn't know they were deliberately imitating them.
My pic taken through the window today is of a couple of mourning doves sheltering from the cold on my verandah, which faces south. I think that's a junco on the snow behind them.
