The departure of the Ruby-throated Hummingbird from Connecticut marks the start of an astonishing migratory journey. As the only hummingbird that breeds in the eastern United States, this tiny avian marvel travels thousands of miles to warmer climates for the winter. The distance covered by a creature weighing only a fraction of an ounce is a remarkable biological achievement, driven by instinct. The timing of this exodus is precise, dictated by environmental shifts that signal the end of the breeding season.
The Primary Departure Window
The southbound migration typically begins in late summer, with activity dropping around late August. Adult males, having completed reproductive duties, are often the first to depart. This initial wave is followed by females and newly fledged juveniles, who undertake the journey on their own.
The peak departure continues through September. By the middle of the month, the majority of the local breeding population has left the state. While most birds are gone by early October, late-season travelers migrating from further north may still pass through. A sharp decline in sightings by mid-October confirms the main migratory flow has passed.
Environmental Triggers for Migration
The decision to migrate is not based on a single factor like a sudden drop in temperature. Instead, the primary biological cue is the photoperiod, or the decreasing number of daylight hours as summer turns to fall. This predictable change in sunlight acts as an internal alarm, triggering hormonal shifts within the birds. These hormones initiate the instinctive urge to migrate and the necessary preparation for the long journey.
This innate programming ensures the hummingbirds begin their migration before local food sources become too scarce or the weather becomes a threat. While colder temperatures and declining flower nectar availability play a supporting role, they serve as secondary cues. The internal biological clock, set by the reducing daylight, compels the birds to leave.
Preparing for the Long Journey
In the weeks leading up to departure, hummingbirds enter hyperphagia, an intense feeding frenzy. They consume greater quantities of nectar and small insects to accumulate energy reserves. A typical Ruby-throated Hummingbird may gain up to 40 percent of its body weight, nearly doubling its mass from about three grams to over five grams.
This added mass is stored as yellow fat, an extremely efficient fuel source for sustained flight. Fat provides more than twice the energy per gram compared to carbohydrates or protein. Homeowners can assist these travelers by keeping nectar feeders clean and fully stocked into the fall. It is recommended to leave feeders up for at least two weeks after the last sighting to ensure late stragglers have access to fuel.
The Winter Destination and Return
The wintering grounds stretch from southern Mexico through Central America to northern Panama. This journey requires them to cover distances of up to 2,000 miles, making them long-distance migrants relative to their body size. A remarkable feat of endurance is the non-stop flight across the Gulf of Mexico, a 500-mile stretch that can take 18 to 22 hours.
The birds spend the winter months in these tropical regions, utilizing the abundant flowers and insects. After resting and feeding, the hummingbirds start their northward migration in the spring. Travelers usually begin arriving back in Connecticut in late April or early May, ready to establish territories and begin the breeding season.