The Ruby-throated Hummingbird, a small bird with a vibrant appearance, undertakes an annual migration. Males typically display an iridescent ruby-red throat, contrasting with their emerald green back, while females are green above with whitish underparts. Known for their rapid wing beats and hovering flight, these birds are the only hummingbird species that breed across eastern North America. Their journey highlights their adaptability and endurance.
The Annual Journey: Timing of Migration
Ruby-throated Hummingbirds begin their northward journey in late February to early March, reaching southern states like Texas and Louisiana. Their arrival progresses further north into the United States throughout April and May, eventually reaching their breeding grounds in northern states and Canadian provinces by late May. Male hummingbirds typically lead this spring migration, arriving a few days earlier than females to establish territories.
The southbound fall migration usually begins in August or September, though some individuals may start as early as July. Adult males are the first to depart, followed by adult females, and then the juvenile birds hatched during the summer. This staggered departure helps ensure varied food availability along their routes. Peak numbers of migrating hummingbirds are often observed in early September.
Signals to Depart: What Triggers Migration
Migration for Ruby-throated Hummingbirds is influenced by several environmental and physiological cues. A primary factor is the changing photoperiod, or the decreasing length of daylight hours, which signals the approaching colder seasons. This reduction in daylight triggers hormonal changes, initiating migration.
Declining food sources, such as nectar from flowers and the availability of insects, also play a role in prompting their departure. As these resources become scarcer, the birds are prompted to move to warmer climates. These signals guide the hummingbirds’ instinct to migrate.
The Incredible Flight: Routes and Destinations
Ruby-throated Hummingbirds primarily spend their winters in Central America, with their range extending from southern Mexico down to Panama. Some individuals also winter along the U.S. Gulf Coast and the southern tip of Florida. Their migratory routes involve many birds undertaking a non-stop flight across the Gulf of Mexico.
This trans-Gulf crossing covers approximately 500 miles and can take between 18 to 22 hours of flight. While many choose this direct route, especially in spring, some hummingbirds follow coastal overland paths around the Gulf, particularly during fall migration. During their journey, these birds typically fly alone and during daylight hours, except for the Gulf crossing which may extend into the night.
Preparing for the Long Haul: Pre-Migration Behaviors
Before migratory flights, Ruby-throated Hummingbirds engage in hyperphagia, significantly increasing their food intake. They consume large quantities of carbohydrate-rich nectar and sugar water, alongside numerous small insects that provide essential fats and proteins. This intense feeding period allows them to build up substantial fat reserves, which are crucial for fueling their long journey.
A hummingbird can nearly double its body weight during this time, accumulating energy-rich yellow fat. For example, a 3-gram hummingbird might gain an additional 2 to 2.5 grams of fat. This stored fat serves as an efficient fuel source, enabling them to fly for hundreds of miles without needing to refuel. Protein from insects also helps strengthen their flight muscles, preparing them for migration.