The Ruby-throated Hummingbird is the only species of hummingbird that breeds in the eastern half of North America, including Pennsylvania. These tiny, iridescent birds spend the summer months in backyards and gardens across the state before embarking on a massive migration. Weighing only about three grams, they fly thousands of miles to warmer climates, driven by an innate biological calendar. Understanding this annual departure involves looking at the specific timing, the environmental cues that trigger the trip, and the journey itself.
The Specific Timing of Departure in Pennsylvania
Migration from Pennsylvania typically begins in late summer and peaks throughout September. While a few adult males may start their journey as early as late July or the first half of August, the majority of the population remains until the end of the breeding season. Adult males, having completed their reproductive duties, are the earliest to depart.
Females and newly fledged juveniles follow a few weeks behind the males, with their numbers peaking during the middle of September. Residents generally see hummingbirds consistently through the end of the month. Although the bulk of the population is gone by October, a few late stragglers, often juveniles, may be observed into the middle of October.
Triggers for Migration
A hummingbird’s departure is not dictated by a sudden drop in temperature. The primary cue is the photoperiod, the steady decrease in daylight hours after the summer solstice. This shortening day length acts as an internal biological signal that triggers hormonal changes within the bird’s body.
The change in light compels the hummingbirds to enter hyperphagia, a state of intense feeding. They consume enormous amounts of nectar and insects, allowing them to gain substantial body fat, sometimes nearly doubling their body weight for fuel. This biological imperative drives their departure, regardless of how warm a particular day in September might be.
The Destination and Journey
Hummingbirds leaving Pennsylvania travel south toward the Gulf Coast of the United States. Many birds funnel along the coasts of Texas and Louisiana before continuing their journey. Their final destination is the wintering grounds, which stretch from southern Mexico down through Central America, reaching as far as Panama.
The most impressive feat of this migration is the non-stop flight across the Gulf of Mexico, a distance of approximately 500 miles. To complete this challenging leg, which can take 18 to 22 hours of continuous flight, the birds rely entirely on the fat reserves they built up before leaving. While some individuals follow a land route around the Gulf, many take the direct water-crossing route.
Helping Late Migrants
Residents can support these travelers by maintaining sugar-water feeders well into the fall. Since migration is triggered by light and not a lack of food, leaving a feeder available will not delay departure or cause the bird to risk freezing. Instead, it offers a necessary fuel source for late-migrating females and inexperienced juveniles who are still building their fat reserves.
Keep feeders clean and filled through the entire month of October, or until the first hard frost occurs. A hard frost depletes the natural floral nectar sources. Providing this readily available energy ensures that any exhausted or late-passing hummingbird has the sustenance required to complete its flight south.