Thanks, guys.
Found a pretty thorough article about the ruby-throats, which is mostly what I seem to have, and their migration habits.
http://www.hummingbirds.net/migration.html
Apparently, it's not unusual for them to head south by mid-September. According to the article, if I keep seeing birds between now and October, it's probably tourists traveling down from farther north, instead of my usual summer residents.
As I'm typing this, I just remembered something anomalous that happened recently, and not just
this summer, but last year, too. And come to think of it, it may be about the last time I noticed a bird both summers. Both times, one of the little guys had been at my feeder when I was on the patio, and then, instead of blasting away as usual, he dropped down almost to eye level facing me, hovering, and darted side to side several times before flying away. Darn if I don't think he was saying good-bye. (And thanks for all the
fish sugar water.)