One of our Advanced Master Gardeners sent this article to post:

courtesy of http://www.hummingbirds.net/map.html
As of Wednesday, March 26, migrating hummingbirds have moved into lower Tennessee and into North Carolina. You can follow their progress on this website: http://www.hummingbirds.net/map.html.
For our area, the rule of thumb is to put out feeders on Tax Day and remove them on Halloween. The last hummingbird I saw was on Oct 1, 2013, but I kept the feeders up until Oct. 31.
Remember to use a 4:1 ratio of water to sugar: Add ¼ cup white sugar to 1 cup of boiling water and allow the nectar solution to cool before filling the feeders. Any leftover solution can be refrigerated for up to a week, but try to change the solution in the feeders every few days.
DO NOT add food coloring or dye to the solution! Studies have shown that food coloring can be detrimental to the hummingbirds.
Providing this food for them as they migrate through entices them to stick around until they can supplement their food source with nectar from Cardinal Flower, Columbine, Coral Bells, Guara, Liatris, Rose of Sharon, Zinnia, and many other flowers.