Migrations are the seasonal movements of animals between their summer breeding grounds and their winter habitats. Other than the leaves turning from green to gold, red and orange, I can think of nothing in nature that signals the change of seasons from summer to fall more clearly or remarkably.
As recently as last week, I was speaking with birders in both Franklin and Clinton Counties who still have hummingbirds visiting their feeders. Both were inquiring as to whether or not their hummingbird feeders should be left up or put away for the season. The thinking is that all hummingbirds should be southbound by now, and that removing the feeders will encourage stragglers to get a move on.
Worldwide, there are well over 300 species of hummingbirds; all of them in the western hemisphere. The ruby throated hummingbird (Archilochus colubris) is the only species found in eastern North America. Like all hummingbird species, ruby throated hummingbirds are solitary creatures; neither living nor migrating in flocks. And, since it's generally believed that all hummingbird migration is prompted by decreasing daylight and probably not at all influenced by changes in temperature or the availability of food, removing feeders will not encourage them to leave. Likewise, leaving feeders out will not keep them here. However, since they are here, and because they need to fatten up if they are going to survive the long journey south, there is no reason not to go on feeding them. In fact, several sources recommend leaving feeders up until two weeks after the last hummingbird is seen feeding.
In order to sustain enough energy to support their elevated metabolisms, hummingbirds must consume nectar, either from suitable flowers or from sugar water solutions in feeders. But nectar is not their only food. Like all living creatures, they need protein. And, while they do receive some dietary protein from pollen that gets stuck to their tongues and bills while drinking flower nectar, in order to get the amount of protein necessary to remain healthy, an adult hummingbird must eat several dozen insects and / or spiders daily. And they are amazingly adept at snatching insects out of the air or from spider webs, off of leaves and flowers, and out of holes left in trees by sapsuckers. In fact, before heading south, hummingbirds will often gorge themselves on insects in order to put on the sustaining layer of fat needed to nourish them through the journey.
There is very little available research about hummingbird migration. And for good reason! To study migration, you need to capture and band large numbers of individual birds. But hummingbirds are nearly impossible to catch. For starters, they're able to fly at speeds of up to 60 miles an hour. And they can rotate their wings, at the shoulder, in a complete circle, so they're able to fly in any direction?- up, down, sideways, backwards - and to change direction instantly or maintain a stationary position in mid-air for prolonged periods of time. In fact, they can fly upside-down and perform rollover maneuvers if attacked by another bird.
Even if you were able to capture and band a large group of individual hummingbirds, what do you think the odds are of locating and recapturing those birds once they're thousands of miles away? To the best of my knowledge, a ruby throated hummingbird has never been banded at a summer nesting site and recaptured in its overwintering grounds, or vice-versa. In fact, as far as I can tell, of the ruby throated hummingbirds that have been captured and banded, only a very few have ever been recaptured. And all of those, with scant few exceptions, were recaptured within 10 miles of the original banding site.
The second available option for studying bird migration involves attaching transmitters to individual birds. A transmitter small enough to attach to a bird weighing 3.5 grams does not exist.
What we do know is this. Males typically start their northbound migration before females do. By most accounts, the same holds true when migrating south for the winter. What's more, late departures are not uncommon among immature birds. And often, due to illness or injury, an individual bird will be unable to leave on schedule. Certainly, a recovering hummingbird preparing for a 2000-mile journey south will appreciate any source of nectar it can find, especially as nectar-producing flowers become scarce. It's also very likely that a hummingbird at your feeder now is not one that was there in mid-summer. It's more likely a bird that has arrived from a summer nesting site in Canada and is just passing through.
Another possibility is tied to basic survival instincts. Bird migrations are often spread out over prolonged periods of time so hurricanes or any other catastrophic weather event or natural disaster that may be encountered on route will not annihilate the entire species. Whatever the reason, you can be sure that a hummingbird coming to your feeder late in the season will appreciate the nourishment and be thankful for a little extra sustenance received before departure, or during a pit stop along the way.
One last thought, as much as I get a kick out of the idea that hummingbirds will hitch a ride on the backs of other, larger migrating birds, geese for example, there is not a single shred of evidence to support this quirky, albeit imaginative and eccentric notion.