Hummingbirds are among the smallest birds on Earth, yet they undertake ambitious migrations. The vast majority of species that breed in North America are neotropical migrants, flying thousands of miles to spend the winter in warmer regions. This high-energy journey is driven by the necessity of finding a reliable food supply to survive the temperate zone’s winter scarcity.
The Seasonal Cycle: Departure and Return Timing
The primary factor determining when hummingbirds leave their northern breeding grounds is the subtle change in daylight hours, known as photoperiod, rather than the immediate drop in temperature or food availability. Decreasing daylight triggers hormonal shifts within the birds, signaling the impending need to migrate south. The southbound departure window for most migratory species, such as the Ruby-throated Hummingbird, generally opens in late summer and early fall, typically beginning in August and peaking in September.
The timing of the journey is not uniform across all individuals, as males often begin their southward trek earlier than females and juveniles. Males can depart as early as mid-July after their breeding duties are complete, while females and young birds follow in the subsequent weeks. Conversely, the return journey north begins in the spring, with the earliest arrivals reaching the southern United States as early as February or mid-March, with males once again pioneering the route.
The Wintering Grounds
The destination for most North American migratory hummingbirds lies in the tropics, where floral resources remain abundant throughout the winter months. For species that breed in the eastern half of the continent, like the Ruby-throated Hummingbird, the winter is spent primarily in southern Mexico and Central America, with documented locations extending as far south as Costa Rica and Panama. These regions provide the necessary warm, high-humidity climate and a continuous supply of flowering plants and insects.
Western species, such as the Rufous Hummingbird, also travel to Mexico for the winter, with some populations reaching areas as far south as Acapulco. The specific ecological zones they choose can vary, with some preferring the lowlands and others, like the Broad-tailed Hummingbird, overwintering in the highlands of Mexico or Guatemala. These environments must sustain their high metabolism, requiring the perpetual availability of nectar and small arthropods.
The Incredible Journey and Navigation
The migration itself is an extraordinary physical undertaking, covering distances of up to 2,000 miles or more, depending on the species and their breeding range. For a bird that weighs only a few grams, the distance is proportionally one of the longest migrations of any bird species globally. To prepare for this arduous journey, hummingbirds engage in hyperphagia, a period of excessive feeding that allows them to gain significant fat reserves, sometimes increasing their body weight by 25 to 40 percent.
This stored fat is the fuel for the most famous part of the Ruby-throated Hummingbird’s journey: the non-stop flight across the Gulf of Mexico, a distance of at least 500 miles. This crossing can take approximately 18 to 22 hours of continuous flight, expending the entire fat reserve they accumulated before departure. Some individuals, however, choose the longer, safer route by following the coastline to reach their winter destinations.
Hummingbirds are highly adept navigators, flying alone without the guidance of a flock and relying on a complex set of innate and learned skills. They are believed to sense the Earth’s magnetic field, potentially using specialized proteins in their eyes as light-sensitive magnetic sensors to orient themselves. They also utilize the sun, stars, and visual landmarks to maintain their course. They possess an impressive spatial memory, allowing them to recall specific, successful feeding locations from previous years.
Species That Stay Put
While most species migrate, a few North American hummingbirds have adapted to remain in milder regions year-round, primarily along the Pacific Coast. The Anna’s Hummingbird is the most prominent example of a non-migratory species that has successfully expanded its range northward, sometimes reaching as far as southern British Columbia. This species has managed to thrive in colder climates by employing specific survival strategies.
When temperatures drop, the Anna’s Hummingbird enters a state of torpor, a regulated hypothermia that dramatically lowers its body temperature and metabolic rate, essentially a nightly mini-hibernation. This adaptation conserves the immense amount of energy that would otherwise be required to maintain their high body temperature during long, cold nights. They also adapt their diet, supplementing winter nectar sources with small insects and even tree sap, which they may find at holes drilled by sapsuckers.