I don't know how this possibly worked for the northern mockingbird. One full moon I stood and listened to one call continuously for an hour and I couldn't reme

I don't know how this possibly worked for the northern mockingbird. One full moon I stood and listened to one call continuously for an hour and I couldn't remember hearing the same call twice. Every bird I'd ever heard in person and more mimicked...several car alarms..sirens... Do they even have their own distinctive call?