This is a common email question we get. I hope by posting here with an answer, it will help others find the answer when searching:

I live in the USA. I hope you can help me identify a bird I have never seen or heard of before. It sings very loudly and it sounds like it is mimicking other local bird songs. I heard the song repeatedly. We even heard it singing loudly at 1:30 am once. There were very different tones, pitches, and even songs. A few times it sounded as though it was mimicking a car alarm. Anyone have any ideas as to what the bird could be??
Your bird is a Northern Mockingbird, which often sing at night and as their name suggests, they mimic other birds. You can often hear shorebird and raptor sounds which often gives a clue as to where the bird has previously been. Here's some more information (scroll down the page to find mockingbird)
Ford (Europe) Model C history