The Ruby-throated Hummingbird is the primary species found east of the Mississippi River, while the Rufous and Allen’s Hummingbirds are common in the West. These tiny birds, known for their dazzling colors and aerial acrobatics, undertake an astonishing annual migration. Their journey southward is driven by biological signals that guide them thousands of miles to wintering grounds in Mexico and Central America. Understanding their departure involves recognizing the natural calendar hardwired into their system.
The Primary Migration Trigger
The primary signal for a hummingbird to begin its journey is not a dip in temperature or a scarcity of food. Instead, migration is initiated by a change in photoperiod—the steady decrease in daylight hours as summer turns to autumn. This reliable environmental cue acts upon the bird’s internal biological clock, triggering hormonal shifts that prepare the bird for long-distance flight. This innate restlessness, known as zugunruhe, prompts the bird to focus entirely on flight preparation.
This biological drive ensures birds depart before cold weather or food shortages become a threat. Diminishing daylight signals that the time for nest-building and raising young is over, regardless of temporary food abundance. While food availability and weather can influence the exact departure day, the decision to migrate south is fixed by the shortening days.
Timing By Region and Species
The departure window for hummingbirds varies depending on their species and breeding location. Ruby-throated Hummingbirds, the most common species in the East, begin their southward movement in late August and continue through September. Birds in the northernmost states and Canada are usually the first to depart, often leaving by the end of August or early September.
Migrants in the Mid-Atlantic and Central states usually see their local breeding population depart throughout September, with a surge of transient birds passing through afterward. Adult males often begin their migration first, sometimes a week or two before the females and juveniles. The last of the Ruby-throats typically cross the southern U.S. border by late October.
On the West Coast, the timing is often earlier, particularly for the Rufous Hummingbird. Rufous Hummingbirds may begin their southbound journey from Alaska and the Pacific Northwest as early as July, traveling down the Rocky Mountain chain. Allen’s Hummingbirds, another western species, also migrate south relatively early, though many coastal Southern California populations are non-migratory or move only to lower elevations for the winter.
Preparing for the Journey
Before migration, hummingbirds enter a state of intense feeding known as hyperphagia. During this period, the birds spend a greater portion of their day consuming nectar and insects to rapidly build up energy reserves. The primary goal of this feeding is to accumulate fat, which is the most efficient fuel source for long-distance flight.
Hummingbirds convert sugar from nectar directly into migratory fat stores, sometimes doubling their body weight before departure. This fat is stored around the body cavity and organs, yielding more than twice the energy per gram compared to burning carbohydrates. For Ruby-throated Hummingbirds flying non-stop across the Gulf of Mexico, this stored fat provides enough fuel for a continuous flight of up to 600 miles.
Managing Feeders During Migration
A frequent concern is the misconception that leaving feeders out will cause hummingbirds to delay or skip their migration. This is incorrect because the migration trigger is the photoperiod, not the availability of food. A healthy hummingbird will depart when its internal clock signals it is time, regardless of a full feeder.
Homeowners are encouraged to keep their feeders clean and filled throughout the fall to support the migrating population. Feeders provide a supplementary source of energy for transient birds or local individuals completing hyperphagia. The most helpful practice is to leave the feeders up for at least two to three weeks after the last hummingbird has been sighted. This ensures that late stragglers, young juveniles, or unexpected transient species have access to the fuel needed to complete their journey.