It's a myth that a hummingbird, or any bird for that matter, will be deterred from heading south in the fall because of human-provided food. Instinct and hormonal urges are what drive birds to migrate, and hummingbirds are no different. Besides, there is good reason to leave your nectar feeder up and full of fresh sugar water until the temperature dips to below freezing, even if you haven't seen a hummer for weeks: It will offer late migrants a refueling spot long after most nectar-producing flowers have ceased blooming. Late-to-migrate hummingbirds turn up throughout North America each fall and winter. By providing a food source, you'll be helping them, not harming them.