The Ruby-throated Hummingbird (Archilochus colubris) is the only hummingbird species commonly found in Maine, present throughout the summer months. These tiny, iridescent birds travel north to the state each spring to take advantage of the seasonal abundance of nectar and insects for breeding. Their presence is strictly seasonal, making migration south an annual necessity as the cold weather and scarcity of food in winter would make survival impossible in the northern climate. This journey is a feat of endurance for one of the smallest migratory animals in the world.
Timing of the Maine Departure
The southward migration begins in a staggered fashion, with adult male hummingbirds being the first to depart from Maine’s breeding grounds. Males generally start their solo journey in mid-to-late August, shortly after reproductive duties are complete. Females and recently fledged juveniles follow suit, typically starting their migration in early to mid-September.
The majority of the local population will have left the state by the middle of September, making late August and early September the peak departure period. While this timing is consistent, local weather patterns can cause slight variations. A sudden cold snap or early frost may accelerate the departure of the final stragglers.
The occasional bird, perhaps migrating from further north, may pass through Maine into late September or even the beginning of October. These later sightings are usually transient birds stopping briefly to refuel before continuing their long-distance flight.
Biological Triggers for Migration
The impulse to migrate is determined by an internal clock responding to an environmental cue, not by food availability or temperature. The primary indicator that initiates the southward journey is the photoperiod: the steady reduction in daylight hours after the summer solstice. This decreasing light triggers hormonal changes within the hummingbird’s body, signaling the need to prepare for the arduous flight.
This physiological shift prompts a period of intense, compulsive feeding known as hyperphagia. During this time, the birds rapidly consume vast amounts of nectar and small insects, often feeding for a greater portion of the day than usual. The purpose of this feeding frenzy is to accumulate a significant layer of body fat, which serves as the high-energy fuel for the migration.
A hummingbird preparing for migration can increase its body weight by 25 to 40 percent. This stored fat is an efficient fuel source, providing more than twice the energy per gram compared to carbohydrates or protein. Researchers estimate these fat reserves can power a non-stop flight of up to 600 miles.
The Route and Destination
The destination for Maine’s Ruby-throated Hummingbirds is the tropical forests of Central America and Southern Mexico, with many overwintering as far south as Panama. The entire migration route is a journey of thousands of miles, undertaken completely alone, as these birds do not travel in flocks.
The most impressive segment of the journey occurs when the birds reach the Gulf Coast of the United States. Here, many individuals choose to make a non-stop flight across the Gulf of Mexico. This crossing is a test of endurance, covering approximately 500 to 600 miles over open water.
This continuous flight can take between 18 and 22 hours, depending on weather conditions, and there is no opportunity to rest or refuel. The birds rely solely on the fat reserves they built up in Maine to power this aerial marathon. Other hummingbirds may opt for an overland route, following the coastline of the Gulf and through Mexico, allowing them to stop and forage along the way.
Supporting Hummingbirds Before They Leave
Maine residents can assist these migrants by providing reliable sources of high-energy food before their departure. It is important to keep feeders filled for at least two weeks after the last hummingbird sighting. This provides a resource for late-departing local birds and transients passing through from further north.
The sugar water solution should be maintained at a ratio of one part plain white granulated sugar to four parts water, mimicking the natural nectar concentration. This solution must be kept fresh and clean. Feeders require washing and the solution must be changed at least once a week, or more frequently in warmer weather, to prevent mold or fermentation.
In addition to feeders, planting late-blooming native flowers offers natural nectar sources for the birds’ final fueling phase. Species like Spotted Jewelweed (Impatiens capensis), Cardinal Flower, and Bee Balm are excellent choices that provide the energy needed for the long flight south.