The Ruby-throated Hummingbird (Archilochus colubris) is the only species that regularly breeds in New Hampshire, making its seasonal movements highly anticipated. As summer ends, these small birds prepare for one of the longest migrations undertaken by any bird its size. Understanding their departure timeline and the science behind it helps residents know when to expect their final visit.
The Core Departure Window
The southward migration begins in waves, with adult male hummingbirds being the first to depart New Hampshire. Having completed their breeding duties, males typically start their journey in late August. This early departure allows them to secure resources farther south before the bulk of the population arrives.
Female hummingbirds and juveniles follow a few weeks later, with their departure peaking in early to mid-September. The majority of the local population has left the state by the end of September. Any sightings after this period are usually late-migrating individuals passing through from areas farther north.
What Signals the Need to Migrate
The primary trigger for the fall migration is not a sudden drop in temperature or a lack of flowers, but a change in the environment’s light cycle. This biological signal, known as photoperiod, is an internal clock that recognizes the progressive shortening of daylight hours. This signal operates independently of local food availability.
Once the photoperiodic signal is received, the birds enter a phase called hyperphagia, where they feed intensely to gain weight. During this time, a hummingbird can nearly double its body weight by accumulating fat reserves. This stored fat is a highly efficient fuel source, which is then metabolized to power the long, strenuous flight ahead.
The Journey South: Destination and Route
The destination for Ruby-throated Hummingbirds leaving New Hampshire is their wintering grounds, which stretch from southern Mexico down into Central America. This journey covers immense distances, with some individuals flying over 2,000 miles one way. Their small size makes this one of the most remarkable migratory feats.
A significant portion of the route involves a non-stop flight across the Gulf of Mexico, a distance of approximately 500 miles over open water. The fat reserves built up during hyperphagia are designed to provide the energy needed for this continuous flight, which can take between 18 and 22 hours. Other birds may follow a longer, more coastal route around the Gulf, allowing for stops to refuel.
Practical Advice for Feeders
Residents often wonder if leaving feeders up will cause hummingbirds to delay their migration, but this is a common misconception. The biological trigger of shortening daylight hours overrides any local food source, ensuring the birds depart on schedule. Maintaining feeders will not prevent a bird from leaving and is beneficial.
It is helpful to keep feeders clean and filled well past the main departure window to assist late travelers or stragglers that may be passing through. A practical guideline is to leave a nectar feeder out until at least mid-October, or until you have not observed a hummingbird for two weeks. Providing this late-season energy source can give a boost to the final birds making their way south.