Hummingbirds, particularly the Ruby-throated Hummingbird, are a common sight in Wisconsin during warmer months. These tiny, iridescent birds, known for their rapid wingbeats and hovering flight, are not year-round residents. As seasons change, they undertake an impressive migratory journey south.
Typical Departure Schedule
Hummingbirds in Wisconsin begin southward migration as early as mid-August. Adult male Ruby-throated Hummingbirds often leave first, sometimes before their breeding season concludes. Females and juveniles typically follow weeks later, ensuring their young are strong enough for the journey. This staggered departure means the exodus from Wisconsin is not a single, sudden event, but a gradual process over several weeks.
The peak departure period is generally throughout September. By this time, many birds have commenced their journey towards wintering grounds in southern Mexico and Central America, with some venturing as far as southern Florida. Most migrating hummingbirds have departed the state by mid-October. Each hummingbird migrates independently, following its own internal cues.
Environmental Factors Influencing Migration
Hummingbird migration is primarily triggered by environmental cues, not a fixed date. A key factor is decreasing daylight hours, or photoperiod. As days shorten in late summer and early fall, this signals winter’s approach and time to migrate. The angle of sunlight also plays a role.
Falling temperatures also contribute to the migratory impulse, as hummingbirds are sensitive to cold. A reduction in natural food sources, such as nectar from flowering plants and insects, prompts their departure. As flowers fade and insect populations decline, it becomes difficult for hummingbirds to meet their high energy demands. These environmental signals activate their migratory instincts.
Preparing for the Journey
Before migration, hummingbirds undergo physiological and behavioral changes. They enter hyperphagia, an intense period of increased feeding. They consume large quantities of nectar and small insects, often feeding from dawn until dusk, to rapidly accumulate fat reserves. Fat is an efficient fuel source for their journey.
A hummingbird can nearly double its body weight, increasing from approximately 3 grams to over 6 grams, in preparation for migration. This stored fat provides energy for long, non-stop flights, including crossing the Gulf of Mexico, which can take 18-22 hours. This preparation is driven by an instinctual migratory restlessness that cues them to begin their journey.
Addressing Late Departures
While most hummingbirds depart Wisconsin by mid-October, some individuals linger later. These late departures can be due to individual variation or abundant food sources. Mild weather or available feeders do not prevent migration; birds rely on internal biological clocks and environmental cues to trigger their departure, not solely on food availability.
Hummingbirds departing exceptionally late face increased risks. Sudden cold snaps or early frosts reduce natural food sources, making sustenance harder. Late-staying individuals may encounter harsher conditions along their migratory route. Observing a hummingbird in Wisconsin in late fall or early winter is rare, typically a straggler or out-of-range species, not a resident Ruby-throated Hummingbird attempting to overwinter.