Ruby-throated Hummingbird at feeder
Ruby-throated Hummingbird at Salvia "Black and Blue" flowers
Ruby-throated Hummingbird at Salvia "Lady in Red" flowers.
Conventional wisdom says hummingbirds will not be detained by feeders, they know when to go. A hummingbird's migration urge is triggered by hormonal changes that respond to decreasing day length. But you still need to determine when to stop filling the feeders and take them down.
When and if you remove feeders depends on where you live in the country. If you live on the West Coast, Anna's Hummingbird can be found all year. There are places in the Southwest and along the Mexican border where a few species of hummers can be found in winter. If you live in the northern part of the country, such as here in NH, the vast majority of Ruby-throated Hummingbirds are gone by the middle of Oct. If you live in some of the states in the middle section of the country, such as Kentucky, most Ruby-throated Hummingbirds have gone through by the end of Oct. If you live in the Southeast in a place like Florida you could possibly have overwintering Ruby-throated Hummingbirds. In addition a number of western species of hummingbirds such as Rufous, Broad-tailed, and Calliope Hummingbirds might show up.
Interestingly there seems to be an increasing trend in western hummingbird species, such as Rufous and Allen's Hummingbirds and others, showing up outside of their normal range in fall in eastern states. NH has had a Rufous Hummingbird in 2007 and 2009 and a Calliope Hummingbird in 2013. They came to feeders but disappeared in the winter.
One of the issues of attempting to host an unusual hummingbird in areas that experience cold and harsh winters is the commitment it takes and the uncertain outcome. A standard hummingbird nectar solution of one part sugar to 4 parts water will freeze below 27 degrees. People go to lengths to warm the nectar such as attaching a flood lamp in a clamp-on reflector a few feet from the feeder, or hanging a low watt heat lamp rigged in an outdoor hanging fixture, but that will only keep the nectar unfrozen to near zero degrees. Last winter NH saw weather below zero. Remember to always keep your hummingbird feeders clean and fresh, mold can grow easily in them if you do not clean them every several days.
Our answer as to when we take the hummingbird feeders down here in NH is that we take our feeders down at the first hard frost. At that point our many hummingbird attractant flowers, such as red Salvia, succumb to the cold, and the hummingbirds are essentially gone from here.
A great place to see which and when hummingbird species are seen in your area, and to report your sightings, is the ebird website. Look under "explore data.
Here are a few photos of rare hummingbirds that have shown up in our state of NH.
The above photo is a Rufous Hummingbird (Selasphorous rufous) visiting a feeder in Hollis, NH in Oct. 2009. This is a very unusual hummingbird for here. One was last reported in NH in 2007. The Rufous Hummingbird is a western species whose breeding range goes as far up as Alaska. Increasingly, Rufous Hummingbirds are showing up in fall in the eastern half of the country. This hummingbird was banded over the weekend and the bander reported it as a hatching year Rufous Hummingbird, sex could not be determined. Identification of female and immature hummingbirds can be tricky, especially telling Rufous from Allen's Hummingbirds. Sometimes only banders, holding them in hand, can tell them apart by subtle differences in the shape of the tail feathers and even then sometimes it is not possible to definitively tell their sex. The above photo shows the extensive rufous on the sides and rufous on the tail feathers.
The throat has lines of small marks, with a number of larger marks (looking dark because the sun is not hitting them) concentrated in the center and going out to the sides of the throat. Usually the immature female rufous has smaller and fewer throat marks, occasionally with a few larger iridescent marks confined to the center of throat.
The back shows little rufous coloring on this bird. Some immature male Rufous Hummingbirds can show more rufous back coloring, especially later in winter. Adult male Rufous Hummingbirds often have extensive rufous on their backs and their throats.
Good luck with your hummingbirds.