We have had three Ruby-throated Hummingbirds at our sugar-water feeder for the past month. We've seen three individuals at the same time, thus our count. We might instead have more, with individuals coming and going. Anyway, this comment assumes the same three birds are being seen. When it was warm, there was much aggression on display. One hummer, a first-fall male I think, guarded the feeder passionately, chasing the other two birds whenever they approached to feed. This was consistent behavior until the weather turned cooler and wetter. Now, the birds quietly share the feeder, two at a time, at ports on opposite sides of the feeder bowl. They also now feed while perched, something rarely done in warmer weather. Feeding then was done on the hover. The birds also feed quite late in the day, one sitting there night before last at 7:30 p.m., when under a cloudy sky the bird could barely be seen from our window 12 feet from the feeder. My guess is that the need for nourishment on cooler damp days and in the morning after cold nights has taken precedence over defense of the food source. Such defense is common among this species. Here are photos of two individuals. I'm not certain of sex or age, but I think these show two of the three. We've had an adult male here this fall as well, with the full ruby throat, but he's not appeared recently.
Just in case you wonder, no, feeding hummingbirds will not compromise their instinct to migrate. And, I replenish the nectar lately much more efficiently than in the past. I've done away with precise measurements of sugar and water. I now pour sugar into the nectar bottle until eyeball measurement shows one-fifth of the bottle is filled, then add cool water and shake. That provides the one-to-four formula recommended, at least close enough, I'm certain, to please the birds. And the sugar dissolves in cool water as readily as it does in hot. I do thoroughly clean both bottle and dispenser with hot soapy water before refilling. I make certain that any traces of mold are gone.