when do hummingbirds fly south for the winter
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Hummingbird
Hummingbirds are birds native to the Americas and comprise the biological family Trochilidae. With about 360 species, they occur from Alaska to Tierra del Fuego, but the vast majority of the species are found in the tropics. They are small birds, with most species measuring 7.5–13 cm (3–5 in) in length. The smallest extant hummingbird species is the 5 cm (2.0 in) bee hummingbird, which weighs less than 2.0 g (0.07 oz).
The largest hummingbird species is the 23 cm (9.1 in) giant hummingbird, weighing 18–24 grams (0.63–0.85 oz). They are specialized for feeding on flower nectar, but all species also consume flying insects or spiders.
Hummingbirds split from their sister group, the swifts and treeswifts, around 42 million years ago. The common ancestor of extant hummingbirds is estimated to have lived 22 million years ago in South America. They are known as hummingbirds because of the humming sound created by their beating wings, which flap at high frequencies audible to humans.
They hover in mid-air at rapid wing-flapping rates, which vary from around 12 beats per second in the largest species to around 80 per second in small hummingbirds. Of those species that have been measured during flying in wind tunnels, their top speeds exceed 15 m/s (54 km/h; 34 mph). During courtship, some male species dive from 30 metres (100 ft) of height above a female at speeds around 23 m/s (83 km/h; 51 mph).
Hummingbirds have the highest mass-specific metabolic rate of any homeothermic animal. To conserve energy when food is scarce and nightly when not foraging, they can go into torpor, a state similar to hibernation, and slow their metabolic rate to 1/15 of its normal rate.
About Hummingbird Migration
Even though hummingbirds are the smallest birds in the world, their migrations can span hundreds or thousands of miles. While there are more than 300 hummingbird species, only a handful of them regularly migrate. Most of the hummingbirds of North America do migrate seasonally between northern breeding grounds and southern wintering grounds.
Unlike many birds, however, hummingbirds migrate individually and do not travel in seasonal flocks. They migrate during the day, staying low in the air to watch closely for feeding opportunities, and rest at night.
Backyard birders who have fed hummingbirds for years quickly learn that these flying jewels can be very predictable with their migration patterns. Individual birds often migrate at the same time each year, even arriving and leaving the same yards within just a day or two. But how do they know when it is time to migrate?
When Hummingbirds Migrate
Several factors affect hummingbird migration and when exactly these small birds set forth on their long journeys. The most important factor that determines the timing of hummingbird migration is daylight: the amount of daylight and the angle of the sun relative to the bird’s location.
As the light levels change seasonally, hummingbirds purposefully eat more, increasing their weight by 25 to 40 percent through hyperphagia, when their hormones change to compel them to gain weight. That extra fat will be valuable energy for their upcoming long flight.
The Fall Migration Triggers
Although there are differing views in the birding community as to what triggers the start of fall migration, it is generally thought that hummingbirds sense changes in daylight duration, and declining numbers of flowers, nectar and insects.
Instinct, their internal biological calendar, and cooling weather conditions also play a role in making the decision to migrate.
Making the Trip South
During migration, a hummingbird’s heart beats up to 1,260 times a minute, and its wings flap 15 to 80 times a second. To support this high energy level, a hummingbird will typically gain 25-40% of their body weight before they start migration in order to make the long trek over land, and water.
They fly alone, often on the same path they have flown earlier in their life, and fly low, just above tree tops or water. Young hummingbirds must navigate without parental guidance, or previous flight experience.
Hummingbirds fly by day when nectar sources such as flowers are more abundant. Flying low allows the birds to see, and stop at, food supplies along the way. They are also experts at using tail winds to help reach their destination faster and by consuming less energy and body fat.
Research indicates a hummingbird normally can travel as many as 23 miles in one day. At that rate it can take several weeks to reach their wintering grounds from summer breeding grounds in the northern U.S. or southern Canada. But in certain circumstances, like the journey over the Gulf of Mexico, they can fly for more extended lengths of time, like 22 hours, nonstop!
While some hummingbirds begin their fall migration as early as late July, most don’t start their journey south till August or September.
Some End Their Fall Migration in the U.S.
Hummingbirds are overwintering on the Gulf Coast in greater numbers than in the past, and many can be found at feeders in South Texas and South Louisiana during mild winters.
For example, in South Louisiana, several species are often spotted during the winter months, including the Ruby-throated, Rufous, Black-chinned, Buff-bellied, Calliope, Allen’s, Broad-tailed, and Broad-billed.
A few hummingbird species are year-round residents in the warmer Pacific coastal and southern desert regions of the United States. Among these are Anna’s hummingbird, a common resident from California inland to Arizona and north to British Columbia.
How Long to Leave Up Hummingbird Feeders?
During the fall migration, it is recommended that hummingbird lovers leave up their feeders for about two weeks after they sight their final bird. Just to feed those late-migrating hummers!
Fall Migration Patterns of Common Hummingbird Species
Of the Pacific Northwest hummingbirds, Anna’s is the only one that doesn’t always migrate south to warmer areas in winter.
The Continental Divide is host to the greatest number and diversity of western migrating hummingbirds. This provides consistent tail winds to support migration.
Rufous, Calliope, and Black-chinned Hummingbirds migrate north up the valleys and along the foothills of the Pacific slopes of the western United States, sipping nectar from spring flowers.
As the lowland flowers begin to die off, the birds move up in elevation to the alpine meadows of the Rocky Mountains and Sierra Nevada where the flowers are in full bloom. Then they follow the mountains of the Continental Divide south to Mexico in late summer and fall.
Natural Food Sources
Hummingbirds will move along their migration routes as food sources appear and disappear. The most important food source is nectar-producing flowers, but the availability of insects is also a factor that can influence when hummingbirds migrate and how fast they travel. This is especially true in spring when abundant insects are a key food source for hummingbird hatchlings to get enough protein for healthy growth.
Weather Patterns
Local storms and strong winds can impact hummingbird migration to a minor degree, delaying the birds’ journeys by a day or two. During poor fall weather, migrating hummingbirds may hang out in safe locations for up to a week or two to wait for better traveling conditions.
Age
Mature birds often start their migration earlier than juvenile birds. Younger hummingbirds take longer to build up their new strength and maturity before setting forth on the long migration journey. Birds that hatched earlier in the year may migrate slightly earlier as well, compared to broods laid later in the breeding season.
Bird Sex
In some hummingbird species, such as the ruby-throated hummingbird, males migrate a few days before females. This gives the male birds time to establish territories so they can successfully court arriving females at the beginning of the breeding season. They follow the same pattern for fall migration to establish winter territories.
Total Migration Distance
The further hummingbirds have to migrate, the sooner they start their journey. The rufous hummingbird, for example, has the longest migration of any hummingbird species—traveling between Mexico and Alaska. And it may begin migrating long before other hummingbird species are traveling.
In spring, hummingbirds may begin flying north as early as January, taking several months to travel to their breeding grounds. And they arriving by mid-May at the northernmost parts of their range. In the fall, some species begin migration as early as July. Though most hummingbirds don’t begin their southward movements until late August or mid-September.
Helping Migrating Hummingbirds
Backyard birders can take several steps to help migrating hummingbirds. It is one of the most common bird feeding myths that feeding hummingbirds will prevent them from migrating. This simply is not true. In fact, savvy birders put their hummingbird feeders up early in the spring and keep them up late in the fall. So the birds have a ready food source no matter how local flowers are blooming. Other ways to help migrating hummingbirds include:
- Planting flowers to attract hummingbirds with a natural food source. They including both early and late blooming flowers for ample nectar in the spring and fall
- Providing nesting materials during spring migration for breeding hummingbirds to quickly and easily build nests to raise their young
- Taking steps to keep hummingbird nectar from freezing in the late fall so it is still available to late-migrating hummingbirds
- Keeping hummingbird feeders clean and replacing spoiled nectar with fresh sugar water regularly. So it will be safe and healthy for hungry hummingbirds
- Supporting conservation initiatives and habitat preservation in hummingbirds’ winter grounds. So they will have safe territories on both ends of the migration
Knowing when hummingbirds migrate gives birders a migration timeline to anticipate when they will see these beautiful birds. And they taking steps to help them will ensure successful migrations for generations of hummingbirds to come.
