I brought in the last of the hummingbird feeders this morning; I guess summer is really gone. (Of course, the fact that the trees are fast becoming naked might be a good indication, too.) Seems kinda late to be taking them down, but we saw a visitor to the feeders when we came back from vacation, and the hummingbird.net FAQ says hummers migrate based on hormonal changes triggered by the changing day length, not by declining food availability. They recommend keeping feeders up for a week or two after you last see visitors, for any birds that are migrating through. The site also has a map of the first sightings in this year's northbound migration; Chicago's first bird was reported in mid-April. Gotta get those feeders out earlier next year!