This year they came early! Or, so it seems anyway. We put out their feeders earlier, too, so maybe we just attracted them earlier, huh? We marked this year's return to Southern New England on April 30th. Could be they were here even earlier, but we just put out the feeders a day or two before that, so.....
Anyway, the hummers apparently have a unique, working system between the males and females; and their specific roles along the migratory routes. And what a route it is!!
Here in New England, we see mostly the Ruby-Throated Hummingbirds. Originally 'tropical' birds, they evolved when the ice sheets receded from the North American continent. They began spreading northward to avoid the tropical hummer-megalopolis!
There is a very informative, more complete, and interesting account of the migratory habits and patterns of these fantastic little creatures at:

http://www.hummingbirds.net/migration.html