The Ruby-throated Hummingbird (Archilochus colubris) is the species most commonly observed across Kentucky, representing the only hummingbird that nests and breeds in the eastern half of North America. These visitors are not year-round residents of the Bluegrass State, but spend the warmer months here before embarking on their annual southward migration. Their presence is purely seasonal, making the timing of their fall departure a significant event for observers across the state. This journey is a response to environmental changes that signal the end of the breeding season.
The Critical Departure Timeline
The autumn migration of hummingbirds out of Kentucky begins in late summer, well before the arrival of cold weather. Adult male Ruby-throated Hummingbirds, having completed their breeding duties, are the first to depart, often starting their journey as early as late July or early August. This early exit allows them to secure resources along the migration route before the larger waves of birds begin moving south.
The females and the young of the year follow several weeks later, typically around mid-to-late August and into September. The peak period for observing migrating hummingbirds passing through Kentucky occurs from late August through the middle of September. By the end of September, the majority of the local and transient populations have moved out of the region.
While most hummingbirds are gone by the first week of October, a few late stragglers or birds migrating from territories farther north may occasionally be sighted. These late-season travelers can sometimes remain in the area until mid-to-late October, especially if the weather remains mild. Sightings after the beginning of November are unusual and often indicate a rare vagrant species that has strayed from its normal western migration route.
Migration Triggers and Destinations
The impulse to migrate is not primarily driven by dwindling food sources or cooling temperatures, but by a biological mechanism responding to light. The main environmental cue for the southward journey is the shortening of daylight hours, known as the photoperiod. This reduction in light triggers hormonal changes in the birds, compelling them to prepare for departure.
In preparation for the energy expenditure required for migration, hummingbirds enter a phase called hyperphagia, a period of intensive feeding. During this time, the birds consume large quantities of nectar and small insects to accumulate fat reserves, which serve as the fuel for their long flight. It is not uncommon for a hummingbird to gain up to 40% of its body weight in fat before setting off, providing the necessary energy for a non-stop journey.
The ultimate destination for the Ruby-throated Hummingbirds leaving Kentucky is their wintering grounds in Mexico and Central America. Many individuals fly south to the Gulf Coast, where they stage for one of the most perilous parts of the journey: a non-stop flight across the Gulf of Mexico. This requires the birds to fly approximately 500 to 600 miles over open water to reach the Yucatán Peninsula and beyond.
Preparing for Their Absence
A common question is when to remove feeders, often out of concern that keeping them stocked will prevent the birds from leaving. This concern is unfounded, as the instinct to migrate is controlled by the photoperiod and fat reserves, not by the availability of sugar water. Feeders should be maintained and kept full well past the time when local birds have departed.
Keeping feeders clean and filled into late fall provides a valuable resource for the later-migrating females and juveniles, as well as birds passing through Kentucky from northern states. A good general practice is to leave feeders up for at least two weeks after the last hummingbird sighting. This ensures that any last-minute travelers have access to a high-energy meal.
For those in Kentucky, keeping a feeder up until at least mid-to-late October is recommended to support these transient birds. Even if the feeder is not being used, the sugar water must be changed every few days to prevent spoilage and maintain a clean food source. Providing this support does not interfere with their natural instincts but offers a helpful stopover point for travelers.
The Return Journey
The birds’ seasonal cycle completes with their return in the spring. The first Ruby-throated Hummingbirds, primarily adult males, typically begin arriving back in Kentucky in mid-to-late April. These early arrivals immediately begin establishing territories and foraging for available nectar sources.
A few sightings may occur as early as the last week of March, particularly in the warmer, southern portions of the state. Females follow the males by about one to two weeks, arriving to select mates and begin the nesting process. The appearance of these birds each spring signals the renewal of the breeding season in Kentucky.