In the world of hummingbirds, around the world, very few hummingbird species are true migrants. In the US and Canada, all of our hummingbirds migrate with the exception of the Anna's hummingbird in Southern California and the Allen's hummingbird - which lives on the Channel Islands – also in California.10
Anna's hummingbirds that do not migrate are called “residents.” Some Anna's hummingbirds have small, east-west migration patterns. A core population of Anna's hummingbirds fly up into the Santa Monica Mountains to breed in the winter and then spread out east into the meadowlands during summer.2 Another population of Anna's reverses this movement and will spend winters in Arizona and summers in California.10 A few have been seen in Canada and Florida – but not in numbers enough to call a migrant population.
Another of our US hummingbirds has a limited or “sedentary” migration range. The Costa's hummingbird will breed in the Colorado Desert to take advantage of the winter and spring rains that bring nectar rich flowers. In the dry heat of summer, they travel to the California coast.2
Our most famous travelers are the Rufous, ruby-throated and calliope hummingbirds. They all nest
in the north and travel great distances every year to reach their southern homes. The ruby-throated hummingbird lives throughout the East Coast and is famous for crossing the Gulf of Mexico. The calliope hummingbird is famous for being the tiniest of all birds who make long migrations.
The Rufous hummingbird is famous for ranging the farthest of any of the hummingbirds. A 2,000 mile journey takes them from their winter homes in Mexico to breeding grounds in the Pacific Northwest, the coast of Alaska and into Canada. They spend most of the year traveling from one to the other and must start their return south as early as July.2
Rufous, calliope and Allen's hummingbirds take a migration route north and south through the mountains and deserts of the West Coast. This route is usually called the ”Pacific Flyway” or “floral highway.” Nature has provided a progression of blooming hummingbird flowers that open in stages as the birds travel along the highway. Floral timing paces the migration. The flowers need the hummingbirds for pollination and the hummingbirds feed on the rich nectars. Their interdependence is one of nature's wonders.8
In the spring, migrating hummingbirds tend to travel north along the US coast and up through the Sierra Nevada Mountains. They reach the Northwest in early summer. In the fall, when the hummingbirds return, their floral highway is inland so they travel south through the Rocky Mountains – along the eastern slopes of the Continental Divide. The high mountains catch precipitation leftover from the monsoon rains – providing a wave of late summer flowers that feed the hummingbirds.11
In the late summer, five or six species of flowers that are only pollinated by birds will open all at one time. We call them “flocks” of flowers. In the spring, bird pollinating flowers only open individually or in sets of two.8 The cornucopia of summer/fall flowers may be organized by nature to provide the extra fuel that the hummingbirds need while taking advantage of their presence to pollinate and seed for next year.
The Continental Divide is host to the greatest number and diversity of migrating hummingbirds. It also causes a number of meteorological events. One of them is to create a swirling of winds around a high pressure dome called the “Great Basin High.” The winds circle clockwise and match the long and narrow looping route that the hummingbirds follow. This provides rather consistent tail winds to support their travels and, more importantly, not hinder them.
On occasion, the size of the high pressure system grows into a “super high.” A super high pressure system can extend over all of the United States and cause endless blue skies and warm weather surrounded or contained by a circle of winds.
Dan True is a meteorologist and hummingbird photographer and he has proposed that a migrating hummingbird could travel the circle winds created by a super high as far as 1,200 – 2,400 miles before the high disintegrated. He has used this theory to explain the consistent presence of Rufous hummingbirds on the East Coast. He believes that some Rufous hummingbirds may be in a state of constant migration traveling farther and with more purpose than we have imagined. Hummingbirds are often reported flying through the mountains at 200 feet and occasionally 300 feet above ground – taking advantage of the Great Basin winds. On super-high winds, they may be able to migrate in a full coast-to-coast circle, hopping the tail winds and foraging along the way.11
Another theory is that the high numbers of Rufous hummingbirds on the East Coast happens because migration signals in young Rufous hummingbirds have broken down. Scientists have proposed that Rufous hummingbirds are vulnerable to being disoriented by wind storms and instead of heading south, they head east until they reach the ocean – where they are in peril as winter sets in.13
Many other species of birds and young hummingbirds find themselves blown off-course and have exceptional systems to correct themselves. I find it hard to believe that there are so many faulty Rufous hummingbirds. Perhaps, like the migration of the ruby-throated hummingbird, they do something “impossible” we have not yet considered.
An accepted fact that is not a theory shows that some Rufous hummingbirds have evolved. There is a documented shift in their migration pattern. A significant population now winters in the United States - along the Gulf Coast between Florida and Texas. They no longer return to Mexico. A change in habitat may be the determining factor that has attracted them. The Gulf Coast used to be forested. Now it is host to flowering shrubs and herbs.
One theory explains the new “winter home” developed because lost or misdirected Rufous hummingbirds found refuge when they reached the East Coast and finally turned south. They did not perish from their mistake and may have passed the new migration destination on to their young. No one is quite sure what the migration pattern is for this new population or how it came to be.2
The range and “home” territories of hummingbirds in North America are changing. The frequency of sightings cannot be explained as a growth in human awareness and interest. Hummingbirds search endlessly for food and every new resource is remembered. As habitat is destroyed and invented, they adapt. One of the new sources of food is landscaping of our cities and homes10 — and so for once, nature is flying closer to us instead of away.