I've wondered, how do you really know it's the same bird? We lived in southern CA for a quite a while. Hummingbirds would hang around during summer, then disappear for a few days to about a week in October. Then they'd show up again. I always thought the ones who showed up after the pause, were from up north, moving to a warmer area towards winter time, and that ours had gone south. Then sometime in February, there would be another week's pause, and hummingbirds were at the feeder again (heading north).