Depending on where live, you may see some hummingbirds well after freezing temperatures have chased most hummingbirds south! It never ceases to amaze me that these little dynamos survive for days in freezing temperatures but they do. If you still have hummingbirds in your area, don’t take your feeder down. The hummingbird needs a reliable and depenable food source on which to help it fatten up for several days before leaving. Eventually, hummingbirds do get sick and too old to make the journey. I don’t know how you would tell the difference between a late migrant and a hummingbird that isn’t going to finish the journey so leave those feeders up just in case.
Hummingbirds can go into a state known as torpor during cold temperatures. This is astate very similar to hibornation. In this state, they might appear to be dead. Entering this state allows the hummingbird to conserve energy. As soon as the bird warms up, it will revive and all of its functions will return to normal. If you find a hummingbird hanging upside down on your feeder in the morning, do not assume that it is dead.
Hummingbirds are tough and hardy creatures and can servive some amazingly tough conditions, including freezing temperatues. Hummingbirds that are able to do so will migrate when it is time for them to do so, but not all hummingbirds migrate. Thus, leaving your feedrs up can provide a vital food source for any hummingbird in need of a meal.