The hummingbird requires a constant supply of energy to sustain its high metabolism. Weighing about as much as a nickel, these tiny birds must consume roughly half their body weight in nectar daily just to survive. When seasons shift, this demand for fuel makes migration necessary, propelling them hundreds or thousands of miles to warmer climates. This journey ensures they can access the continuous nourishment required throughout the winter.
Environmental Triggers for Departure
The timing of the fall migration is not primarily driven by a drop in temperature or a sudden lack of flowers, a common misunderstanding. Instead, the main signal for a hummingbird’s departure is a change in photoperiod, which is the gradual shortening of daylight hours as summer ends. This external cue triggers an internal biological clock, initiating hormonal changes that prepare the bird for its long journey south.
For the Ruby-throated hummingbird, the fall migration can begin as early as late July or August, with the adult males typically departing first, sometimes weeks before the females and juveniles. The migration then continues in waves, with most of the population in the northern parts of their range leaving by the end of September, although stragglers may be seen well into mid-October. Species like the Rufous hummingbird, which breed further north in the Pacific Northwest and Alaska, often begin their southward journey even earlier, sometimes starting in July.
Physiological Preparation for Migration
Once the photoperiod cue signals the approach of migration, hummingbirds enter a state of excessive eating known as hyperphagia. This intense feeding is dedicated to rapidly accumulating the fat reserves that will fuel their flight. A hummingbird typically gains 25 to 40 percent of its body weight, with some individuals nearly doubling their mass before departure.
Stored fat is the primary fuel source for migration, offering more than twice the energy per gram compared to burning carbohydrates or protein. The fat is deposited in specific pockets around the bird’s body and organs, allowing for efficient weight distribution. Fat metabolism is also beneficial because it produces twice as much water as other fuels, which helps protect the birds from dehydration during long, non-stop flights.
The Journey: Routes and Destinations
The migration is a solitary endeavor, with each hummingbird traveling alone rather than in large flocks. For the Ruby-throated hummingbird, the journey often involves a non-stop flight across the Gulf of Mexico, a distance of approximately 500 miles. This segment can take 18 to 22 hours of continuous flight, which is possible due to the fat reserves they have accumulated.
Hummingbirds generally fly at a speed of about 25 miles per hour and use stopovers to refuel on nectar and insects along the way. Most North American hummingbirds, including the Ruby-throated species, winter in southern Mexico and Central America. The Rufous hummingbird follows a different path, migrating south along the Rocky Mountains after breeding further north, covering distances up to 4,000 miles.
Maintaining Feeders During Departure Season
A popular misconception is that keeping a feeder available will cause hummingbirds to delay their migration. Since the primary trigger for departure is the shortening daylight hours, not food availability, an artificial nectar source will not prevent the bird from leaving. Maintaining feeders during the fall is helpful, as it provides an energy source for birds preparing for their journey or those passing through on a stopover.
Keep feeders up for at least two weeks after the last hummingbird sighting in your area. This ensures that any late-season migrants or stragglers have access to a clean meal before continuing south. During this time, keep the sugar solution fresh and the feeder clean, especially as cooler weather arrives.