"It always distresses me to see hummingbird feeder left out in early fall. You may as well shoot them as to keep them here until the first cold snap kills them."
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I don't think there is anything to worry about. If they show up at my place at all, it is in early fall. They stoke up at the feeder for a few days and are gone.

I bet if you checked the literature, you would find that they migrate in response to weather and day length.

Given the destruction of food sources prevalant today, any help they can get on their arduous journey is going to be a help.