If you've done much backyard bird watching, you've probably seen mockingbirds engage in this behavior. I'm guessing they may be vying for winter feeding territories, but I really don't know. When my son was young, he said they were having a political debate. Kids say the cutest things.
(By the way, this is the first time I've tried to post a video to my blog from my hard drive. I attempted several times before it actually posted. Let me know if you are able to view the video, which is only about a half minute video. Thanks.)