Hummingbirds grace Colorado’s landscapes with their vibrant presence each year, performing extraordinary feats during their migratory journeys. These tiny, jewel-toned birds captivate observers with their aerial acrobatics and boundless energy. Their annual arrival signifies spring and summer, transforming gardens and natural areas into bustling hubs of activity. As seasons shift, these remarkable creatures prepare for their long flights south, undertaking impressive migrations.
General Departure Window from Colorado
Hummingbirds typically begin their southward migration from Colorado as early as late July, with peak departures throughout August and September. While some species, like Rufous hummingbirds, may start their journey in mid-summer, most hummingbirds that breed in Colorado begin to leave by early September. Black-chinned hummingbirds usually depart around early September, and Calliope hummingbirds tend to leave by the third week of September.
Broad-tailed hummingbirds, common breeders in Colorado, generally remain longer, often staying until mid-October. Some hummingbirds may even linger into November, and feeders should be kept available until no birds have been observed for a couple of weeks. The latest departures can extend into early October for certain species, marking the typical end of the hummingbird season in the state.
Environmental and Individual Influences on Departure
The precise timing of hummingbird departure from Colorado is a flexible window, influenced by environmental cues and individual factors. Changes in daylight duration are a primary trigger, signaling the end of the breeding season and the need to seek wintering grounds. Declining numbers of flowering plants and insects, which reduce available food resources, also prompt the migratory urge. As autumn advances, temperatures drop, plants enter dormancy, reducing nectar availability, and insects become less abundant, compelling hummingbirds to seek warmer climates.
Individual characteristics also play a role. Adult males often migrate earlier than females, sometimes as early as mid-July, allowing them to establish territories in their wintering grounds. Adult hummingbirds generally depart before juveniles, as younger birds may require more time to build up fat reserves and muscle mass for the journey. Factors such as reproductive success, age, and individual health can influence a bird’s readiness for the demanding migratory flight.
Pre-Migration Behaviors
Before embarking on their long migratory flights, hummingbirds engage in specific behaviors to prepare their bodies for the journey. This intense feeding period, known as hyperphagia, involves consuming excessive amounts of nectar and insects to rapidly accumulate fat reserves. Hummingbirds can consume their entire body weight in sugar water or nectar daily, along with up to 2,000 tiny insects, sometimes doubling their body weight during this phase. This stored fat is crucial, providing more than twice the energy per gram compared to carbohydrates or protein, and also generating water to help prevent dehydration during flight.
Hummingbirds also exhibit increased aggression at feeders and flowering plants, defending prime feeding spots to ensure they acquire sufficient energy stores. The fat is efficiently stored in various areas, including around the wishbone and along the flanks, ensuring their weight is spread evenly for flight. This physiological preparation allows them to undertake journeys that can span hundreds to thousands of miles, often flying alone without parental guidance for juveniles.