The disappearance of hummingbirds from North American backyards each autumn marks one of the most compelling biological events in the Western Hemisphere. These tiny birds, often weighing less than a nickel, undertake astonishing journeys. Their annual migration is an instinct-driven movement that transports these miniature marvels thousands of miles to warmer climates, raising curiosity about how and where they survive the colder months.
Signs That Migration Is Starting
The stimulus for this southward movement is not primarily a drop in temperature, but a change in the amount of daylight. As the days grow shorter after the summer solstice, a reduction in the photoperiod triggers hormonal changes within the birds. This internal calendar signals that it is time to begin preparing for migration.
This physiological signal initiates a period of intense, compulsive eating known as hyperphagia. Hummingbirds spend several weeks feeding aggressively on nectar and small insects to accumulate the necessary fat reserves. This concentrated feeding allows the birds to increase their body weight by 25 to 40 percent, serving as fuel for the migration. The males are the first to depart, often starting their journey as early as mid-July, followed by the females and young birds, with the main southbound push occurring from late August through October.
The Southern Destinations
The destination for North America’s migratory hummingbirds is primarily the warmer regions of Mexico and Central America. The wintering grounds vary significantly depending on the species. The Ruby-throated Hummingbird, which breeds across the eastern half of the continent, typically winters between southern Mexico and northern Panama, utilizing habitats like coffee farms and forest edges.
The Rufous Hummingbird breeds farther north than any other species, with some traveling as far as Alaska. These western migrants follow a clockwise loop down the Rocky Mountains, spending their non-breeding months in southern Mexico. Their primary wintering habitat is in the high-elevation pine and oak forests. Small numbers of both species have also been documented overwintering along the U.S. Gulf and Atlantic coasts.
The Incredible Journey
The migration is powered almost entirely by the fat reserves accumulated during the hyperphagia phase. This stored fat is an ideal fuel source, providing more than twice the energy per gram compared to carbohydrates or protein. The scale of the journey is illustrated by the Rufous Hummingbird, whose 3,900-mile flight from Alaska to Mexico is equivalent to covering over 78 million of its own body lengths.
The most demanding leg of the journey belongs to the Ruby-throated Hummingbird, many of which make a non-stop crossing of the Gulf of Mexico. This over-water flight covers approximately 500 miles and must be completed in a single effort, lasting 18 to 22 hours. While some Ruby-throats opt for a longer overland route around the Gulf, the direct path is a testament to the endurance packed into a bird weighing only a few grams. Facing risks like strong headwinds and storms, the successful completion of this flight is an unparalleled feat.
Resident Hummingbirds
Not all hummingbirds undertake migration, as some populations remain in North America year-round. The Anna’s Hummingbird, for example, is a resident species found along the Pacific Coast, often surviving as far north as southern British Columbia.
To survive the long, cold nights, these resident hummingbirds employ a specialized physiological state called torpor. Torpor is a deep, sleep-like condition where the bird dramatically reduces its metabolic rate by as much as 95 percent. The bird’s body temperature can drop significantly, conserving energy until daylight returns. This state allows the Anna’s Hummingbird to survive when food is less abundant and the weather is severe.