Most folks look to the leaves for the passage from summer to fall. I look to the birds.
hummingbirds flew out the first week of November. I left a feeder up a few weeks longer, just in case, but after a mass sugar drunk of bees, from which two didn't recover and the rest had what must have a been a helluva hangover, because it took them all day to climb out of the feeder ports and fly away, we brought the feeders in for the winter. I was reluctant but the bees were gorging to harmful excess and I don't want to contribute to their demise.
Otherwise, I'd leave a feeder up for late hummingbirds. Last year a Rufous hummingbird spent a few weeks with us in December. Rufous hummers don't live in the Texas Hill Country and theoretically don't migrate through. But we've had a stray every fall-winter since we moved here. We react as if we're new parents--notices to the neighbors and all that. I put on extra coffee in case anyone wants to come down and watch the flying-orange show.
Rufous hummingbird photo courtesy of Gary Woodburn's Flikr photo-stream.
Until we moved to the Hill Country, we knew one species of sparrow by sight. All others were LBJs, Little Brown Jobs. Now we know nine, because they're our neighbors, living markers of time and season.