Ruby-Throated Hummingbird migration is prompted by hormones, not weather. Go ahead and leave those feeders up as a nectar source for the stragglers coming from the north. Especially since flower sources begin to dwindle during the fall season in most home gardens.
For more fun facts, check out this entertaining and informative video, below. Or, click on this How to Attract Hummingbirds to your Garden link.